Bolthole Index

Mercer County, Ohio

Building permits, zoning and land rules in Mercer County, Ohio

42Index Score / 100
#66 of 88 in Ohio

Unincorporated Mercer County, Ohio requires a zoning permit for most construction, but that approval is separate from any residential building-code review12. Celina and the Village of Coldwater set their own zoning34. The Mercer County Health District handles septic siting, lot approval and permits for every address5.

At a glance

Building permit
Zoning permit required for most construction where the county code applies6
Zoning
County code applies in its unincorporated jurisdiction; local administration varies elsewhere78
Septic permits
Health District approval and permit required for new, replacement or altered systems9
Lot size
80 acres in A-1, 20 acres in A-2, 1 acre in A-R10
Agricultural buildings
No zoning certificate for qualifying agricultural structures, with a platted-subdivision exception11
Owner-builder
Building-code submissions and inspections are waived only where no certified residential department has jurisdiction12
Minimum home size
900 sq. ft. in a county residential zone, with an exception for approved efficiency apartments13
Private wells
Local board-of-health permit required before most construction or alteration14
Floodplain development
Special flood-hazard permit comes before the zoning permit in mapped hazard areas15

Who to call

Zoning

Mercer County Planning Commission

Zoning-permit applications, zoning-map amendments, subdivision applications and access to the county zoning code

(419) 586-6402

janellw@mercercountyoh.gov

220 W Livingston St, Celina, OH 45822

Septic permits

Mercer County Health District

Household sewage treatment system siting, lot approvals, permits, operation and maintenance review, and nuisance investigations

(419) 586-3251

220 W Livingston St, Suite B152, Celina, Ohio 45822

Roads & driveways

Mercer County Engineer

County and township road engineering, utility and driveway permits, and floodplain administration

(419) 586-7759

4884 Mud Pike, Celina, OH 45822

Contact details are copied from each office’s official page and were checked against it on October 14, 2026.

Off-grid gear

Going off-grid in Mercer County means bringing your own water and power. The kit we’d start with:

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Do you need a building permit in Mercer County, Ohio?

Yes where the Mercer County Zoning Code applies, but the county approval is a zoning permit, not necessarily a residential building-code permit. The zoning permit covers construction, structural alterations, moving buildings, changed uses, accessory structures, fences, signs and swimming pools in the governed unincorporated area1617. Qualifying agricultural buildings and structures need no zoning certificate, except in a platted subdivision of 15 or more lots of 1 acre or less1811. Ohio's residential code is uniform wherever a certified building department enforces it, but we could not confirm which certified department, if any, covers an ordinary house on a given Mercer County parcel2. Inside Celina and the Village of Coldwater, the municipality's own zoning applies instead of the county code34. Ask the Planning Commission to identify both the zoning authority and any residential building-code authority before work begins19.

Who is the Mercer County building department, and who issues permits?

Start with the Mercer County Planning Commission at 220 W Livingston St, Celina, OH 45822, or call (419) 586-6402 for the zoning-permit application and county zoning code19. Building-code inspection depends on certification, and the county's pamphlet identifies state building-inspector coverage for commercial buildings, manufactured homes and residential buildings of three or more units; we could not confirm who inspects a single-family house, so ask Planning before submitting plans2019. Zoning fees vary by application type, must be paid before action is taken, are payable by cash or check and are nonrefundable; ask Planning for the current amount21. The Mercer County Health District handles septic matters at (419) 586-3251522. The Mercer County Engineer reviews county-road driveway and utility permits at (419) 586-775923.

Does Mercer County have zoning?

Yes. The Mercer County Zoning Code divides the governed unincorporated area into districts and regulates land, structures and uses there177. Local administration varies across the county, so confirm the parcel's authority and mapped district before applying a dimensional rule824. Minimum lots are 80 acres in A-1 Prime Agriculture, 20 acres in A-2 Agriculture and 1 acre in A-R Agriculture/Residential10. A-1 requires 75-foot front, 50-foot side and 60-foot rear setbacks; A-R requires 50, 20 and 30 feet25. Height is capped at 35 feet in all three, and A-R limits lot coverage to 20%2627. In a county residential zone, a dwelling generally needs at least 900 square feet of floor area, 22 feet in both width and length, and a permanent foundation; approved efficiency apartments are excepted13.

How do septic permits work in Mercer County?

The Mercer County Health District handles septic-system siting, building-lot approval, permitting, operation and maintenance review, and nuisance investigations under Ohio Revised Code Chapter 3718, inside and outside city limits528. A board-of-health permit is required before installing a new or replacement system or altering an existing one; the application requires an approved site review, and a registered installer must do the work9. Soil evaluations are required on any new building lot, before replacing a system and at minor-subdivision parcel split-offs, and system type and size follow the soils2930. The board of health inspects installation before final cover and inspects the finished system again within 12 months31. On a sale, the Health District will inspect a septic system on request, as some lenders require; it asks for tank cleaning if there has been none in the previous 5 years32. Countywide soil data rates 0% of Mercer County soils as free of severe conventional-drain-field limitations, so settle septic feasibility before choosing a house site33. Call (419) 586-325122.

Can you live in an RV or tiny home on your land in Mercer County?

We could not confirm a countywide rule allowing or prohibiting long-term RV residence on private land. Ohio's campground rule governs licensed and temporary campgrounds, not occupancy on an individual private parcel34. We also could not confirm a rule written specifically for tiny homes, but a dwelling in a county residential zone generally must meet the 900-square-foot floor-area minimum and the other dimensional and design standards13. A permanently sited manufactured home treated as a single-family dwelling must likewise have at least 900 square feet and measure at least 22 feet in width and length, excluding additions, along with the listed foundation, utility, design, date and federal-label conditions35. Ask the Planning Commission whether the proposed RV or tiny home is an allowed use in the parcel's jurisdiction and district819.

How do you build a home in Mercer County, step by step?

  1. Ask the Planning Commission to identify the parcel's zoning jurisdiction, mapped district, local inspector and any certified residential building department8363719.
  2. If creating a new parcel, complete the applicable subdivision or lot-split review before treating it as buildable38.
  3. Start the Health District's soil evaluation, site review and septic design before fixing the house location530.
  4. Apply to the local board of health before constructing or altering a private well14.
  5. Ask the County Engineer about driveway access and obtain any required flood-hazard development permit before the zoning permit2339.
  6. Submit the zoning application, fee, site plan and supporting documents; the Zoning Inspector has 30 days to decide a complete application, and the permit is void if work is not started within 1 year or finished within 2 years404121.
  7. If a certified residential department has jurisdiction, follow its plan-review and inspection process; if none has jurisdiction, Ohio's owner-builder rule removes residential-code submission, approval, inspection and occupancy-certificate requirements, but not zoning, septic or other rules4212.

What should you check before buying land in Mercer County?

Verify zoning jurisdiction, septic feasibility, water, flood risk, legal access and any parcel-division approval before closing. Zoning administration varies, and the official map controls the district where the county code applies843. A division involving land below 5 acres may trigger subdivision review, while a qualifying minor subdivision is limited to 5 lots including the original or remaining parcel and must front an existing public road44. Septic deserves early attention because countywide soil data rates 0% of soils as free of severe conventional-drain-field limitations33. Ask the County Engineer about driveway and mapped flood-hazard review2339. If public sewer is accessible and available under Ohio standards, connection can be required instead of onsite disposal45. Mercer County's effective property-tax rate is about 1.1%, and the median annual property-tax bill is about $2,2494647.

Watch-outs

  • A Mercer County zoning permit is not the same as residential building-code review; ask Planning whether a certified residential building department serves the parcel13719.
  • Long-term RV living, tiny-home treatment and accessory dwellings remain unconfirmed; the county residential-zone minimums still apply to a structure treated as a dwelling1319.
  • In a mapped A zone, AE zone or floodway, the special flood-hazard development permit must come before the zoning permit39.
  • The county code says permitted work must begin within 6 months, while the application form voids the permit after 1 year without a start; follow the earlier deadline4041.

Sources

  1. Mercer County Zoning Code, quoted and re-checked
  2. Section 3781.10 | Board of building standards - powers and duties, quoted and re-checked
  3. Celina: Celina Codified Ordinances, Chapter 1180 Supplemental Regulations (American Legal Publishing) (Mercer County), quoted and re-checked
  4. Village of Coldwater: Coldwater, Ohio Zoning Ordinance No. 1661 (August 2017) (Mercer County), quoted and re-checked
  5. Household Sewage Treatment Systems – Mercer County Ohio Health District, quoted and re-checked
  6. Mercer County Zoning Code, quoted and re-checked
  7. Mercer County Zoning Code, quoted and re-checked
  8. Mercer County Zoning Code, quoted and re-checked
  9. Rule 3701-29-09 - Site review and permits for STS installation and operation, quoted and re-checked
  10. Mercer County Zoning Code, quoted and re-checked
  11. Mercer County Zoning Code, quoted and re-checked
  12. Ohio Residential Code of Ohio, Rule 4101:8-1-01, quoted and re-checked
  13. Mercer County Zoning Code, quoted and re-checked
  14. Chapter 3701-28 | Private water systems (Ohio statewide rule), quoted and re-checked
  15. Mercer County Zoning Code, quoted and re-checked
  16. Mercer County Zoning Code, quoted and re-checked
  17. Mercer County Zoning Code, quoted and re-checked
  18. Mercer County Zoning Code, quoted and re-checked
  19. Mercer County Planning Commission (mercercountyoh.gov)
  20. Mercer County Township and Zoning Inspectors, quoted and re-checked
  21. Mercer County Zoning Code, quoted and re-checked
  22. Mercer County Health District (mercercountyoh.gov)
  23. Mercer County Engineer (mercercountyoh.gov)
  24. Mercer County Zoning Code, quoted and re-checked
  25. Mercer County Zoning Code, quoted and re-checked
  26. Mercer County Zoning Code, quoted and re-checked
  27. Mercer County Zoning Code, quoted and re-checked
  28. Household Sewage Treatment Systems, quoted and re-checked
  29. Household Sewage Treatment Systems – Mercer County Ohio Health District, quoted and re-checked
  30. Household Sewage Treatment Systems, quoted and re-checked
  31. Rule 3701-29-09 - Site review and permits for STS installation and operation, quoted and re-checked
  32. Real Estate Inspections, quoted and re-checked
  33. Share of soils USDA rates "not limited" for a conventional septic drain field (SSURGO). A strict rating: the median county is about 6% and a tenth of counties are 0%, so a low figure means most lots need a site evaluation or an engineered system, not that septic is impossible. Cite it only with that caveat: Bolthole Index county data
  34. Rule 3701-26-04 | Campground requirements (Ohio statewide rule), quoted and re-checked
  35. Mercer County Zoning Code, quoted and re-checked
  36. Mercer County Zoning Code, quoted and re-checked
  37. Ohio Residential Code of Ohio, Rule 4101:8-1-01, quoted and re-checked
  38. Mercer County Zoning Code, quoted and re-checked
  39. Mercer County Zoning Code, quoted and re-checked
  40. Mercer County Zoning Code, quoted and re-checked
  41. Application for Zoning Permit, quoted and re-checked
  42. Ohio Residential Code, Rule 4101:8-1-01, quoted and re-checked
  43. Mercer County Zoning Code, quoted and re-checked
  44. Chapter 151 - Subdivision Regulations, quoted and re-checked
  45. Rule 3745-42-07 | Best available technology for connection into sanitary sewers and centralized collection and treatment (Ohio statewide rule), quoted and re-checked
  46. Effective property tax rate: Bolthole Index county data
  47. Median property tax bill: Bolthole Index county data

Written October 14, 2026 from the rules quoted below, each taken from an official source and re-checked by an independent reviewer. This is research, not legal advice: rules change, so confirm with the office before you buy or build.

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Compared with neighboring counties

Like 4 of its 6 neighbors, Mercer County has countywide zoning.

RuleMercer CountyVan Wert CountyAuglaize CountyShelby CountyDarke CountyAllen CountyPaulding County
Building permitRequiredLimitedRequiredRequiredRequiredLimitedLimited
County zoningYesYesYesNoNoYesYes
Septic permitsCounty Health DistrictCounty General Health DistrictCounty Health Dept.Sidney-Shelby County Health Dept.County General Health DistrictCounty Public HealthCounty Health Dept.

County locator

Mercer County in Ohio

42
County map
Mercer County highlighted among the Ohio counties · colored by Index score

How Mercer County scores

Seclusion23100% ev.
Self-Sufficiency30100% ev.
Admin Boringness5390% ev.
Durability77100% ev.
Property Autonomy35100% ev.
Carry Cost58100% ev.

Evidence strength: 98%. This reports direct-source completeness and fallback use; it is separate from the score and is not a confidence interval. How it works →

$280kTypical home
1.1%Property tax
$12,513Land / acre
39.3"Annual rain
0.9% of yrsSevere drought
4.4 / yr (+4.3)Mid-century 100°F days
12.1 daysMid-century dry spell
1.54" (+8.9%)Mid-century 1-day rain
1.81×Wildfire change factor
100%Forward climate coverage
$1,108Home insurance / yr
0.7% / yrInsurance growth
0.15%Nonrenewal rate
county median (2+ published ZIPs)Insurance basis
82,331People within 30 min
6,396,463People within 2 hr
60,066Radius comparison (15 mi)
91.8People / sq mi
0.2%Federal land
99.9%Land at 15% slope or less
0%Soils rated "not limited" for septic (strict USDA rating)
0 acWorkable land screen
6.2%Wooded land
108.3 tonsBiomass / forest ac
51.1°FAvg temp

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Cities and towns in Mercer County

Inside a city, town or township here, that government usually sets zoning and may issue its own building permits; the county’s rules above cover land outside them.

Not yet researched: Black Creek Township · Butler Township · Center Township · Village of Chickasaw · Dublin Township · Village of Fort Recovery · Franklin Township · Gibson Township · Granville Township · Hopewell Township · Jefferson Township · Liberty Township · Marion Township · Village of Mendon · Village of Montezuma · Recovery Township · Village of Rockford · Village of St. Henry · Union Township · Washington Township

Answers from the rulebook for Mercer County

What the ordinances and state agencies actually say — one answer per question, each quoted from the official source and independently re-checked.

Mercer County rules

  • Building permitRequired

    County zoning permit for construction, alteration, movement, establishment, or change of use in the county zoning jurisdiction.

    • Agricultural exemptions apply as defined by the code.
    • Additional approvals may be required for conditional uses, temporary uses, variances, nonconforming uses, and planned-unit developments.
    • The zoning permit is conditional on commencement within 6 months and substantial completion within 2 years under §1147.03; the application form states void if work is not started within one year or completed within two years.

    approval deadline: 30 days (Zoning Inspector must approve or disapprove within 30 days after receipt.)

    “No building or other structure, unless it is exempt as agricultural (see definition), shall be erected, moved, added to, or structurally altered; nor shall any building, structure, or land be established or changed in use; nor shall any accessory structure, fence, sign, or swimming pool be installed without a permit issued by the Zoning Inspector.”
    One more reviewed finding on this topic
    • Required — Erection, movement, addition, structural alteration, establishment or change of use, and specified accessory structures in areas where the Mercer County Zoning Code applies.
      “No building or other structure, unless it is exempt as agricultural (see definition), shall be erected, moved, added to, or structurally altered; nor shall any building, structure, or land be established or changed in use; nor shall any accessory structure, fence, sign, or swimming pool be installed without a permit issued by the Zoning Inspector.”
  • InspectionsLimited

    Building inspections by certified or contracted building-code authorities for covered building types.

    • Certification controls which buildings and subjects may be inspected.
    • The county pamphlet identifies state building-inspector coverage for commercial buildings, manufactured homes, and residential units of three or more.
    “Enforcement authority for approval of plans and specifications and enforcement authority for inspections may be exercised, and plans and specifications may be approved and inspections may be made on behalf of a municipal corporation, township, or county”
  • County-wide zoningPresent (with conditions)

    Zoning in the unincorporated area governed by the Mercer County Zoning Code.

    • Agricultural exemptions apply as provided in the code.
    • Municipal zoning may apply inside incorporated municipalities.
    “No building or other structure, unless it is exempt as agricultural (see definition), shall be erected, moved, added to, or structurally altered; nor shall any building, structure, or land be established or changed in use; nor shall any accessory structure, fence, sign, or swimming pool be installed without a permit issued by the Zoning Inspector.”
    2 more reviewed findings on this topic
    • Present (with conditions) — Buildings, structures, land uses, accessory structures, fences, signs, and swimming pools regulated by the Mercer County Zoning Code in the county jurisdiction where the county code applies.
      “A RESOLUTION OF MERCER COUNTY, OHIO [...] DIVIDING THE COUNTY INTO ZONES AND DISTRICTS”
    • Present (with conditions) — Land, structures, and uses in the unincorporated area where the Mercer County Zoning Code applies.
      “A RESOLUTION OF MERCER COUNTY, OHIO, ENACTED IN ACCORDANCE WITH A COMPREHENSIVE PLAN AND THE PROVISIONS OF THE OHIO REVISED CODE, DIVIDING THE COUNTY INTO ZONES AND DISTRICTS, ENCOURAGING, REGULATING, AND RESTRICTING THEREIN THE LOCATION, CONSTRUCTION, RECONSTRUCTION, ALTERATION, AND USE OF STRUCTURES AND LAND;”
  • Local zoningVaries (with conditions)

    Aggregate of county, township, municipal, and village zoning across Mercer County; the county conclusion does not mean the county administers each local ordinance.

    • The official county pamphlet identifies Jefferson Township and Burkettsville as not zoned; other listed townships and municipalities have zoning-inspector contacts.
    • Parcel-specific applicability must be confirmed with the relevant local zoning inspector.
    “JEFFERSON(WEST) NOT ZONED [...] BURKETTSVILLE NOT ZONED”
  • Zoning districtsPublished (with conditions)

    Mercer County Zoning Code districts.

    • The official zoning map, maintained by the Board of County Commissioners, is stated to be the final authority on current zoning status.
    • The document lists A-1, A-2, A-R, R-1 through R-4, R-C, C, C-L, C-I, I, Q, and SP districts.
    “The following zoning districts are hereby established for Mercer County, Ohio: A-1 Prime Agriculture District A-2 Agriculture District A-R Agriculture/Residential District R-1 Low-Density Residential District R-2 Medium-Density Residential District R-3 High-Density Residential District R-4 Multi-Unit Residential District”
    2 more reviewed findings on this topic
    • Published (with conditions) — Zoning districts and district-specific regulations in the unincorporated area governed by the Mercer County Zoning Code.
      “The following zoning districts are hereby established for Mercer County, Ohio:”
    • Published (with conditions) — County zoning districts and district-specific land-use and dimensional controls.
      “The original and one copy of the official zoning map are to be maintained and kept up to date; one copy on public display in the office of the Board of Mercer County Commissioners, accessible to the public, and shall be final authority as to the current zoning status of lands, buildings, and other structures in Mercer County.”
  • Minimum dwelling sizeSpecified

    Residential uses regulated by the Mercer County Zoning Code, including efficiency apartments and permanently-sited manufactured homes.

    • The 300-square-foot minimum applies to an efficiency apartment in a two-family or multi-family building without a separate distinct sleeping room.
    • The 900-square-foot minimum applies to a permanently-sited manufactured home seeking treatment as a single-family dwelling, and the code also requires a permanent foundation, appropriate utilities, minimum 22-foot width and 22-foot length, minimum 3:12 roof pitch, conventional residential siding, minimum 6-inch eave overhang with appropriate guttering, manufacture after January 1, 1995, and a permanent label or tag certifying compliance with applicable federal construction and safety standards.
    • The cited county code was adopted August 23, 2001, effective September 22, 2001, and includes amendments effective November 22, 2002 and August 21, 2004.

    minimum floor area for efficiency apartment: >= 300 square feet (Two-family or multi-family dwelling unit without a separate distinct room for sleeping.) · minimum floor area for permanently-sited manufactured home: >= 900 square feet (Excluding additions; applies to classification as a single-family dwelling under the cited definition.) · minimum width for permanently-sited manufactured home: >= 22 feet (Excluding additions.) · minimum length for permanently-sited manufactured home: >= 22 feet (Excluding additions.)

    “having a minimum floor area of 300 square feet. [...] has a minimum width of 22 feet [...] and a minimum floor area of 900 square feet;”
    3 more reviewed findings on this topic
    • District specific (with conditions) — Efficiency apartments in two-family or multi-family buildings within the unincorporated areas where the Mercer County Zoning Code applies.
      “having a minimum floor area of 300 square feet.”
    • District specific (with conditions) — Single-family, two-family, and multi-family residential dwellings and accessory buildings located in a Mercer County residential zone within the unincorporated area.
      “a minimum floor area of 900 square feet;”
    • District specific (with conditions) — Permanently-sited manufactured homes treated as single-family dwellings under the Mercer County Zoning Code in applicable unincorporated areas.
      “a minimum floor area of 900 square feet;”
  • Minimum lot sizeSpecified

    Lots in Mercer County zoning districts.

    • Requirements vary by zoning district; the code summary lists A-1 Prime Agriculture as 80 acres, A-2 Agriculture as 20 acres, and A-R Agriculture/Residential as 1 acre.
    • New subdivision lots and metes-and-bounds parcels must conform to the district.

    A-1 minimum lot area: 80 acres · A-2 minimum lot area: 20 acres · A-R minimum lot area: 1 acre

    “A-1 PRIME AGRICULTURE 80 acres** 300’** 75’** 50’** 60’** 35’ N/A A-2 AGRICULTURE 20 acres** 200’** 75’** 50’** 60’** 35’ N/A A-R AGRICULTURE/RES. 1 acre 150’ 50’ 20’ 30’ 35’ 20%”
    One more reviewed finding on this topic
    • District specific (with conditions) — Nonagricultural uses in the I Industrial District.
      “The maximum height and minimum lot requirements within the I Industrial District shall be as follows: Requirements for nonagricultural uses only: Minimum Lot Area 1 acre Minimum Lot Width 200 feet Minimum Front Yard Setback 50 feet”
  • SetbacksSpecified

    Required yards and setbacks in Mercer County zoning districts.

    • Setbacks vary by district.
    • The application requires front, rear, side, and total-side-yard dimensions.

    A-1 front setback: 75 feet · A-1 side setback: 50 feet · A-1 rear setback: 60 feet · A-R front setback: 50 feet · A-R side setback: 20 feet · A-R rear setback: 30 feet

    “Minimum Front Yard Setback (3) Minimum Side Yard Setback (4) Minimum Rear Yard Setback (5) [...] A-1 PRIME AGRICULTURE 80 acres** 300’** 75’** 50’** 60’** 35’ N/A A-2 AGRICULTURE 20 acres** 200’** 75’** 50’** 60’** 35’ N/A A-R AGRICULTURE/RES. 1 acre 150’ 50’ 20’ 30’ 35’ 20%”
    One more reviewed finding on this topic
    • District specific (with conditions) — Nonagricultural uses in the I Industrial District.
      “The maximum height and minimum lot requirements within the I Industrial District shall be as follows: Requirements for nonagricultural uses only: Minimum Lot Area 1 acre Minimum Lot Width 200 feet Minimum Front Yard Setback 50 feet Minimum Side Yard Setback 30 feet Minimum Rear Yard Setback 40 feet”
  • Lot coverageSpecified

    Maximum lot coverage in Mercer County zoning districts.

    • Maximum coverage varies by district; the dimensional table lists N/A for A-1 and A-2 and 20% for A-R.

    A-R maximum lot coverage: 20 percent

    “Max. Percent Lot Coverage (6) [...] A-1 PRIME AGRICULTURE 80 acres** 300’** 75’** 50’** 60’** 35’ N/A A-2 AGRICULTURE 20 acres** 200’** 75’** 50’** 60’** 35’ N/A A-R AGRICULTURE/RES. 1 acre 150’ 50’ 20’ 30’ 35’ 20%”
    One more reviewed finding on this topic
    • District specific (with conditions) — Nonagricultural uses in the I Industrial District.
      “The maximum height and minimum lot requirements within the I Industrial District shall be as follows: Requirements for nonagricultural uses only: Minimum Lot Area 1 acre Minimum Lot Width 200 feet Minimum Front Yard Setback 50 feet Minimum Side Yard Setback 30 feet Minimum Rear Yard Setback 40 feet Maximum Height 45 feet Maximum Lot Coverage 50%”
  • Building heightSpecified

    Maximum building height in Mercer County zoning districts.

    • Height varies by district; the dimensional table lists 35 feet for A-1, A-2, and A-R.

    A-1 maximum building height: 35 feet · A-2 maximum building height: 35 feet · A-R maximum building height: 35 feet

    “Maximum Building Height [...] A-1 PRIME AGRICULTURE 80 acres** 300’** 75’** 50’** 60’** 35’ N/A A-2 AGRICULTURE 20 acres** 200’** 75’** 50’** 60’** 35’ N/A A-R AGRICULTURE/RES. 1 acre 150’ 50’ 20’ 30’ 35’ 20%”
    One more reviewed finding on this topic
    • District specific (with conditions) — Nonagricultural uses in the I Industrial District.
      “The maximum height and minimum lot requirements within the I Industrial District shall be as follows: Requirements for nonagricultural uses only: Minimum Lot Area 1 acre Minimum Lot Width 200 feet Minimum Front Yard Setback 50 feet Minimum Side Yard Setback 30 feet Minimum Rear Yard Setback 40 feet Maximum Height 45 feet”
  • Who permits septicMixed (with conditions)

    Household sewage treatment systems in the Mercer County Health District.

    • The program operates under Ohio Revised Code Chapter 3718 and Ohio Administrative Code Chapter 3701-29.
    • Mercer County HSTS rules are identified as effective May 1, 2021.
    “Household sewage treatment systems are regulated under the authority of Chapter 3718 of the Ohio Revised Code and Chapter 3701-29 of the Ohio Administrative Code.”
    One more reviewed finding on this topic
    • Mixed (with conditions) — Household sewage treatment systems in Mercer County.
      “Household sewage treatment systems are regulated under the authority of Chapter 3718 of the Ohio Revised Code and Chapter 3701-29 of the Ohio Administrative Code. This program covers septic system siting, building lot approvals, septic system permitting, review of system operation and maintenance, and nuisance investigations.”
  • Septic permitRequired

    Septic-system permitting in the Mercer County Health District.

    • The program covers septic-system siting, building-lot approvals, permitting, operation and maintenance review, and nuisance investigations.
    • Soil evaluations are required on any new building lot, before existing-system replacement, and at minor-subdivision parcel split-offs.
    • System type and size depend on soil type and condition.
    “This program covers septic system siting, building lot approvals, septic system permitting, review of system operation and maintenance, and nuisance investigations.”
  • Septic inspectionLimited

    Private septic-system inspections associated with ownership transfers in Mercer County.

    • The inspection is provided upon request.
    • The Health District describes these inspections as sometimes required by financial institutions, not as universally required for every transfer.
    • The septic inspection requires tank cleaning if it has not been cleaned in the previous five years, with documentation.
    • A file search is performed for a permit if applicable.
    • If no problems are detected, the system is cleared for sale regardless of current code compliance and permit status.

    prior septic-tank cleaning period: <= 5 years

    “Upon request, the Mercer County Health District will inspect private water systems (wells) and septic systems as sometimes required by financial institutions for homes in process of transfer of ownership.”
  • Off-grid sanitationLimited

    Off-grid household sanitation using household sewage treatment systems.

    • Soil evaluations are required on new building lots, before existing system replacement, and at minor subdivision parcel split-offs.
    • System type and size depend on individual-property soil conditions.
    • Improper sewage disposal or discharges are subject to Health District nuisance response.
    “Regulations governing septic systems require soil evaluations on any new building lot, prior to existing system replacement, and at the time of minor subdivision parcel split-offs.”
  • Agricultural exemptionConditional

    Agricultural land use and agricultural buildings or structures.

    • The zoning-certificate exception does not apply to a platted subdivision consisting of 15 or more lots of 1 acre or less.

    subdivision-lot threshold: >= 15 lots (platted subdivision consisting of lots of 1 acre or less) · lot-area threshold: <= 1 acre (platted subdivision consisting of 15 or more lots)

    “The Ohio Revised Code confers no power on any County zoning commission, board of County Commissioners, or board of zoning appeals to prohibit the use of any land for agricultural purposes or the construction or use of buildings or structures incident to the use for agricultural purposes of the land on which such buildings or structures are located. No zoning certificate shall be required for any such building or structure except any platted subdivision consisting of 15 or more lots of 1 acre or less.”
    2 more reviewed findings on this topic
    • Available (with conditions) — Agricultural land uses and agricultural buildings or structures incident to agricultural use under the Mercer County Zoning Code.
      “No building or other structure, unless it is exempt as agricultural (see definition), shall be erected, moved, added to, or structurally altered”
    • Available (with conditions) — Agricultural buildings and structures under the Mercer County Zoning Code.
      “No zoning certificate shall be required for any such building or structure except any platted subdivision consisting of 15 or more lots of 1 acre or less.”
  • Subdividing landRegulated (with conditions)

    Subdivision and lot-split review in Mercer County.

    • The zoning code requires new subdivision lots and metes-and-bounds parcels to conform to district requirements.
    • The County Auditor Tax Map Department performs survey and subdivision review; applicable planning-commission and local zoning requirements may also apply.
    “Survey and subdivision review [...] Providing lot split information”
    One more reviewed finding on this topic
    • Regulated (with conditions) — Major and minor subdivisions, parcel divisions, and replats governed by the Mercer County Subdivision Regulations.
      “D. Minor Subdivision – Division of a parcel of land involving no more than 5 lots (inclusive of the remaining or original parcel) any one of which is less than 5 acres, from the original parcel, site, or lot along an existing public street, not involving the opening, widening, or extension of any street or road as defined in these Regulations.”
  • Building in a floodplainRequired

    Development requiring a county zoning permit in an A zone, AE zone, or floodway shown on the Mercer County Flood Insurance Rate Map.

    • No zoning permit may be issued until a Special Flood Hazard Development Permit is issued by the Flood Plain Administrator.
    • The county pamphlet identifies the Mercer County Engineer as Flood Plain Administrator.
    “No zoning permits are to be issued in an A zone AE zone, or floodway as depicted on the Flood Insurance Rate Map (FIRM) for Mercer County until a Special Flood Hazard Development Permit has been issued by the office of the Flood Plain Administrator.”
    One more reviewed finding on this topic
    • Required — Development requiring a zoning permit in an A zone, AE zone, or floodway shown on the Mercer County Flood Insurance Rate Map.
      “No zoning permits are to be issued in an A zone AE zone, or floodway as depicted on the Flood Insurance Rate Map (FIRM) for Mercer County until a Special Flood Hazard Development Permit has been issued by the office of the Flood Plain Administrator.”
  • Permit feesVariable (with conditions)

    Fees for county zoning applications and related administrative procedures.

    • Fees must be paid before action is taken; fees are payable by cash or check and are nonrefundable.
    • The Commissioners set fees for accessory buildings, new dwellings, additions, nonresidential buildings, signs, changes of use, temporary uses, conditional uses, nonconforming uses, variances or appeals, map or text amendments, and planned-unit developments.
    “Until all such appropriate fees, charges, and expenses have been paid in full, no action shall be taken on any application, appeal, or administrative procedure. All fees shall be paid by cash or check and shall not be refundable.”
  • Permit processPublished (with conditions)

    Mercer County zoning-permit applications.

    • The form calls for a sanitary sewer permit number, site plan and building plans in triplicate, zoning-permit fee payment, and any other supplemental requirements or conditions.
    • The permit is void if work is not started within one year or completed within two years.

    start-work deadline: 1 year (or permit is void) · completion deadline: 2 years (or permit is void)

    “This permit shall be void if work is not started within one (1) year or completed within two (2) years.”
    2 more reviewed findings on this topic
    • Published (with conditions) — Mercer County zoning-permit application and approval process.
      “Within 30 days after the receipt of an application, the Zoning Inspector shall either approve or disapprove the application in accordance with the provisions of this Zoning Code.”
    • Published (with conditions) — Mercer County zoning-permit application and approval process.
      “The undersigned applies for a zoning permit for the following use, said permit to be issued on the basis of the information contained within this application. The applicant hereby certifies that all the information and attachments to this application are true and correct.”

Ohio rules that apply here

  • Owner-builder exemptionConditional

    Electrical and heating, ventilating, and air-conditioning work performed as contracting within an Ohio county; the statute authorizes, but does not itself impose, county licensing rules.

    • A board of county commissioners may adopt licensing rules by resolution for electrical and HVAC contractors not required to hold a valid and unexpired Chapter 4740 license.
    • County rules may be enforced in unincorporated areas and in municipalities that contract with the county for enforcement.
    • A county rule may require examinations, technical-skill demonstrations, fees, and additional licensing requirements.
    • A county board may accept a valid and unexpired Chapter 4740 license for construction, replacement, maintenance, or repair of one-, two-, or three-family dwellings or incidental accessory structures.
    • The statute does not establish a statewide owner-builder electrical or HVAC contractor-license exemption; county and municipal rules must be checked for the specific location.
    “Each board of county commissioners may adopt, by resolution, rules establishing standards and providing for the licensing of electrical and heating, ventilating, and air conditioning contractors who are not required to hold a valid and unexpired license pursuant to Chapter 4740. of the Revised Code.”
    4 more reviewed findings on this topic
    • Conditional — Owners of residential buildings in an Ohio jurisdiction where no certified municipal, township, or county residential building department has jurisdiction, including potentially unincorporated Mercer County.
      “If no municipal, township, or county building department [...] has jurisdiction, the owner is not required to make submission of construction documents”
    • Conditional — Owners of one-, two-, and three-family dwellings in areas where no municipal, township, or county building department certified for residential buildings has jurisdiction under Ohio Revised Code section 3781.10(E).
      “If no municipal, township, or county building department is certified [...] has jurisdiction, the owner is not required to make submission of construction documents, seek approvals”
    • Conditional — An owner-builder constructing, erecting, altering, or equipping a building covered by Ohio Revised Code section 3781.06, including residential buildings, where a certified municipal, township, or county building department has jurisdiction.
      “No owner shall proceed with the construction, erection, alteration, or equipment of any building until the plans or drawings, specifications, and data have been approved as this section requires, or the industrialized unit inspected at the point of origin.”
    • Conditional — An owner performing contractor-regulated construction, improvement, or renovation on the owner's own primary residential building in Ohio.
      “(F) "Construction project" means a construction project involving a building or structure subject to Chapter 3781. of the Revised Code and the rules adopted under that chapter, but not an industrialized unit or a residential building as defined in section 3781.06 of the Revised Code.”
  • Building code adoptedAdopted

    Ohio's state residential building code as applicable to residential construction in Mercer County when enforcement is performed by a building department certified for the relevant state residential-code authority.

    • The Ohio Board of Building Standards adopts the state residential building code.
    • Residential-code requirements are uniform in areas with a building department certified to enforce the state residential building code.
    • A county, township, or municipal building department may enforce only the building-code types and subject matters for which it is certified.
    • The source does not establish that Mercer County itself has a certified residential building department or identify the current enforcing department for a particular Mercer County parcel.
    “The board shall incorporate those rules into separate residential and nonresidential building codes.”
    3 more reviewed findings on this topic
    • Adopted (with conditions) — Ohio's Residential Code of Ohio for one-, two-, and three-family dwellings, including Mercer County where a certified residential building department has jurisdiction.
      “The rules governing residential buildings are uniform requirements in any area with a building department certified to enforce the state residential building code”
    • Adopted (with conditions) — Buildings and classes of buildings regulated under Ohio Revised Code Chapter 3781, including residential and nonresidential buildings and industrialized units.
      “The board of building standards shall formulate and adopt rules governing the erection, construction, repair, alteration, and maintenance of all buildings or classes of buildings specified in section 3781.06 of the Revised Code, including land area incidental to those buildings, the construction of industrialized units, the installation of equipment, and the standards or requirements for materials used in connection with those buildings. The board shall incorporate those rules into separate residential and nonresidential building codes.”
    • Adopted — Ohio's statewide residential and nonresidential building codes governing covered building construction, repair, alteration, and maintenance.
      “The board shall incorporate those rules into separate residential and nonresidential building codes.”
  • Manufactured homesLimited

    Occupancy of manufactured homes installed in Ohio and regulated under Chapter 4781 of the Revised Code and implementing rules.

    • A manufactured home generally may not be occupied until the inspector issues the inspection seal.
    • The inspection seal must be paid for when the permit is issued.
    • A temporary occupancy permit may provide the applicable exception under Rule 4781-7-01(C).
    • The home must meet Ohio manufactured-home installation standards; local ordinances and other regulations may also apply to site placement.
    “Except as provided in paragraph (C) of this rule, no manufactured home shall be occupied until the inspector has issued the inspection seal.”
  • Well permitRequired

    Construction, alteration, sealing, or decommissioning of private water systems, including private wells and test wells, in Ohio.

    • A valid permit must be issued by the board of health before construction, alteration, or sealing, except that a person sealing a well or decommissioning a private water system not being replaced must apply no later than five business days afterward.
    • Except where specified exceptions apply, no work may begin until the permit is issued and approved.
    • Applications require the applicable permit fee, required information, and a fee for at least one water sample for alteration, conversion, or new construction.
    • An application becomes a permit upon validation by the local health district.
    • Plans are additionally required for specified systems, including systems serving a building, non-one/two/three-family dwellings, cisterns, springs or ponds, flowing-well areas, drive-point wells, buried pressure tanks, gasoline-powered pumps, continuous disinfection or filtration, and certain point-of-entry treatment systems.

    post-sealing/decommissioning application deadline: <= 5 business days (Applies when the well or private water system is not being sealed or decommissioned because it is being replaced.)

    “No person shall construct, alter or seal a private water system, test well or part thereof, unless a valid permit for the system has been issued”
  • Mandatory utility hookupSewer (with conditions)

    Disposal of sewage where an existing publicly owned or regional sanitary sewer is accessible and available.

    • The sewer connection may not conflict with an areawide waste-treatment plan, approved regional sewage-service and treatment plan, or connection ban.
    • The receiving disposal system must have or be expected to have capacity to collect and treat the sewage.
    • For an existing structure, any part of the structure generating waste must be within 300 feet of the nearest sanitary-sewer right-of-way boundary.
    • For a proposed structure outside a larger common plan, any lot property line must be within 300 feet.
    • For two or more proposed structures, the threshold is 200 feet multiplied by the number of proposed structures, up to 5,000 feet.
    • The director may grant an exemption when technical, financial, environmental, legal, or physical barriers prevent connection and the alternative will not adversely affect human health or the environment.
    • When a sewer later becomes accessible and available, a non-public or non-regional disposal system must generally be abandoned and connection made within three years unless the director authorizes another timeframe.

    existing structure sewer-distance threshold: <= 300 feet (Measured to the nearest boundary of the sanitary-sewer right-of-way.) · proposed structure sewer-distance threshold: <= 300 feet (Measured from any property line of the lot.) · multiple proposed structures threshold: 200 feet multiplied by the number of proposed structures (Maximum distance is 5,000 feet.) · connection deadline after accessibility becomes available: 3 years (Unless an alternative timeframe is authorized by the director.)

    “Connection into existing publicly owned or regional sanitary sewers is required for the disposal of sewage when said sewers are accessible and available.”
  • Campground & park staysLimited

    Roadside camping at designated Ohio state forests along public roads maintained by the division of forestry.

    • Permitted only at designated state forests, along public roads maintained by the division of forestry, during certain legally established hunting seasons.
    • The chief of the division of forestry must authorize the applicable season.
    • Only self-contained camping units meeting Rule 1501:3-3-04 are permitted unless restroom facilities are available.
    • Vehicles must be parked sufficiently far off the roadway not to present a hazard and may not block roads, trails, or gated access areas.
    • Other restrictions in Rule 1501:3-3-06 apply.
    “Roadside camping is permitted at designated state forests, along public roads maintained by the division of forestry, during certain legally established hunting seasons as authorized by the chief of the division of forestry.”
    2 more reviewed findings on this topic
    • Limited — Occupancy and placement of recreational vehicles in Ohio-licensed campgrounds and temporary campgrounds.
      “Recreational vehicles or portable camping units shall be parked only on sites that have been verified as complying with plans approved by the director, or in the case of a temporary campground, by the licensor;”
    • Prohibited — Camping in Ohio state forests outside areas, sites, or campgrounds designated by the chief of the division of forestry or an authorized agent.
      “No person shall camp in a state forest except in areas, sites or campgrounds designated by the chief of the division of forestry or authorized agent.”
  • county zoning authorityGeneral

    County commissioners may adopt zoning resolutions regulating building, structures, land uses, and districts or zones in unincorporated territory statewide.

    • The authority is exercised by resolution and must be in accordance with a comprehensive plan.
    • The authority applies to unincorporated territory of the county.
    • The statute begins with the exception phrase “Except as otherwise provided in this section,” so the limitations in ORC Chapter 303 apply.
    • For nonresidential property only, the county may regulate height, bulk, number of stories, size, lot coverage, yards, courts, open spaces, and population density.
    • Agricultural uses and agricultural buildings are subject to the limitations in ORC 303.21; the statute also contains limitations for public utilities, railroads, telecommunications towers, alcoholic-beverage sales, oil and gas drilling, and permanently sited manufactured homes.
    • Activities regulated under ORC Chapters 1513 and 1514 may be regulated only in the interest of public health or safety, and Chapter 1514 activities must be provided for as permitted or conditional uses as specified by ORC 303.02.
    “the board of county commissioners may regulate by resolution, in accordance with a comprehensive plan”
  • county building authorityGeneral

    County commissioners may adopt and enforce local residential building regulations in unincorporated areas and may operate certified county building departments that enforce state residential and nonresidential building codes, accept and approve plans, and conduct inspections.

    • Local residential building regulations may be enforced within the unincorporated area or within districts established in the unincorporated area.
    • A local residential building regulation may not differ from the state residential building code unless it addresses subject matter not addressed by that code or is adopted under ORC 3781.01.
    • An existing structures code must concern subject matter not addressed by, and may not conflict with, the state residential building code.
    • County building departments may enforce state codes only for the types of buildings and subject matters for which they are certified.
    • Certification permits enforcement authority, plan approval, and inspections; the certification application identifies whether it covers residential or nonresidential buildings and whether residential certification covers new construction only or also repair and alteration.
    • The board may adopt flood-hazard, Lake Erie coastal-erosion, and drainage regulations, subject to the statutory limits and exceptions in ORC 307.37.
    • Local regulations, codes, or amendments require public hearings at not fewer than two regular or special board sessions; they take effect on the thirty-first day after adoption.
    • Regulations adopted under ORC 307.37 generally do not affect buildings or structures existing, or under construction, before adoption, except as provided for an existing structures code.
    • The state residential building code is effective as a uniform requirement in areas with a building department certified to enforce it.
    “The board of county commissioners may adopt local residential building regulations governing residential buildings as defined in section 3781.06 of the Revised Code”
    One more reviewed finding on this topic
    • General — Ohio boards of county commissioners adopting and enforcing local residential building regulations in unincorporated county areas, including districts established within those areas, and administering state building codes when certified.
      “The board of county commissioners may adopt local residential building regulations governing residential buildings”

Set by your township or city, not the county

In Ohio, zoning is adopted by each township or city, so Mercer County has no county-wide answer on these. Find your township or city in the list of places on this page, or call its clerk or zoning administrator.

  • Living in an RV
  • Camping on your land
  • Tiny homes
  • Accessory dwellings
  • Short-term rentals

Still unanswered

We looked and could not find an official answer yet. Silence is not permission — ask the county directly.

  • Certificate of occupancy — Certificates of occupancy for residential structures in Mercer County.
  • Driveway access — Driveway access requirements for development in unincorporated Mercer County.

Each answer was extracted from an official source and independently re-checked against that source by a second reviewer. That is an evidence check, not legal advice. Rules change; confirm with the authority before you buy or build.

Living off-grid in Mercer County, Ohio

Is Mercer County a good place to live off-grid or homestead?

Mercer County scores 42/100 on the Bolthole Index, a marginal county profile. Its strengths: a durable current and mid-century hazard profile and higher long-term carry cost. Watch-outs: about 82,331 people within a 30-minute drive and workable self-sufficiency basics (39.3″/yr rainfall).

Do you need a building permit in Mercer County, Ohio?

Mercer County generally requires a residential building permit, and it enforces county zoning. Onsite septic is permitted by Mercer County Health District. Owner-builders may act as their own contractor to build their home. These answers are quoted from official sources and independently re-checked. Rules change and cities within the county differ — always confirm with the county before you buy or build.

How much does land cost in Mercer County, Ohio?

Land in Mercer County runs about $12,513 per acre, based on the latest county data.

What is the water situation in Mercer County?

Mercer County gets about 39.3" of rain a year, with severe drought in roughly 0.9% of years.

How remote is Mercer County?

A representative private-land location has about 82,331 people within a 30-minute drive and 6,396,463 within two hours. The road-network catchments count population across county lines and clusters of smaller cities; straight-line radius values remain available as a comparison.

How Mercer compares in Ohio

Compare side-by-side →See all 88 Ohio counties ranked →