Bolthole Index

Mercer County, Missouri

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

75Index Score / 100
#28 of 115 in Missouri

Unincorporated Mercer County, Missouri does not require a county residential building permit1. County zoning could not be confirmed, so ask the Mercer County Commission or County Clerk before relying on a parcel for an RV, tiny home, or particular setback234. Missouri DHSS administers onsite-wastewater permits in Mercer County56.

At a glance

Building permit
Not required for a residence in unincorporated Mercer County1
Zoning
Unconfirmed; ask the County Commission or County Clerk before relying on a proposed use234
Septic authority
Missouri DHSS administers onsite-wastewater permits in Mercer County56
Septic permit
Required before most installations or repairs; DHSS must confirm any single-family exemption75
RV or tiny-home living
No Mercer County occupancy rule was confirmed; ask the County Commission or County Clerk234
Owner-builder exemption
A homeowner may install a septic system in some cases, but must ask DHSS and may still need a construction permit86
Septic lot size
State onsite-wastewater law sets no minimum lot size, but subdivision approvals and system setbacks may constrain a site9

Who to call

Also useful

Mercer County Presiding Commissioner

Starting point for county zoning, floodplain, building-inspection, and county-road questions when no dedicated office is listed

660-748-3425

802 E MAIN ST, PRINCETON MO 64673-1240

Also useful

Mercer County Clerk

County records and general administration; a contact for confirming whether a local land-use rule or permit office applies

660-748-3425

802 E MAIN ST, PRINCETON MO 64673-1240

Septic permits

Missouri DHSS Onsite Wastewater Treatment Program

Onsite wastewater treatment system construction permits for Mercer County

(573) 751-6095 ext. 5

OnsiteProgram@health.mo.gov

930 Wildwood Dr, Jefferson City, MO 65102

Online permits →

Contact details are copied from each office’s official page and were checked against it on October 7, 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, Missouri?

Unincorporated Mercer County does not require a county residential building permit1. Missouri authorizes local code adoption rather than imposing one uniform statewide building code, and county authority depends on classification and, in some circumstances, voter approval1011. No Mercer County building-inspection schedule or certificate-of-occupancy requirement could be confirmed, so ask the County Commission or County Clerk about an unusual project or a parcel near city limits34. Missouri separately protects farm buildings and farm structures from permits imposed through county fire-protection or fire-prevention ordinances, but that protection is not a blanket exemption from septic, floodplain, zoning, or other land-use requirements12.

Who handles building and land-use questions in Mercer County?

Mercer County has no confirmed county building department or building inspector, consistent with the county residential building-permit answer1. For an unincorporated parcel, start with the Mercer County Commission or County Clerk to confirm whether a newer county action, floodplain concern, or county-road requirement affects the site34. The Missouri Department of Health and Senior Services administers onsite-wastewater permits in Mercer County56. DHSS directs Mercer County applicants to submit project information through its online form to request an application number6. Do not begin septic work until DHSS issues a permit or confirms an exemption135. A driveway connecting to a state highway is outside county building review; MoDOT requires a permit for construction or modification of a driveway within its right-of-way14.

Does Mercer County have zoning?

Countywide zoning in unincorporated Mercer County could not be confirmed, and no authoritative county source establishes zoning districts or a zoning ordinance2. Missouri law allows counties in specified classifications to establish zoning for unincorporated territory only after the question is submitted to voters and a majority approves it15. That legal pathway does not prove Mercer County adopted zoning. Before buying or laying out a project, ask the Mercer County Commission or County Clerk whether any current rule controls setbacks, minimum lot size, minimum dwelling size, building height, lot coverage, or subdivision of the parcel34. An incorporated city, town, or village may have its own rules because Missouri's framework treats incorporated municipalities separately10.

How do septic permits work in Mercer County?

Missouri DHSS administers onsite-wastewater permits in Mercer County and directs applicants to its request form for an application number56. A construction permit is required before most onsite-wastewater installations or repairs, although some single-family residential lots may be exempt; do not start work until DHSS issues the permit or confirms the exemption75. A homeowner may install the homeowner's own system in some cases, but must check with DHSS, may still need a construction permit, and is strongly encouraged to use a registered installer86. State onsite-wastewater law sets no minimum lot size, but an approved subdivision lot size, system setbacks, and the added space needed for a lagoon can still constrain a site9. Application fees for construction, modification, and repair are temporarily suspended16. Soil evaluation deserves early attention because 0% of Mercer County soils are rated without severe limits for a conventional drain field17.

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

Mercer County's rules for long-term RV occupancy, temporary camping, and tiny-home occupancy could not be confirmed. County zoning itself is also unconfirmed, so a buyer should not treat the lack of a published answer as permission2. Ask the Mercer County Commission or County Clerk about the exact parcel, intended duration of occupancy, utility connections, setbacks, and whether city limits change the answer34. A tiny home used as a dwelling may not need a county residential building permit in unincorporated Mercer County, but that does not settle sewage disposal or occupancy questions1. Onsite wastewater must follow applicable permit rules, and wastewater may not be discharged into a road ditch or onto the ground18.

Building a home in Mercer County: the steps, in order

  1. Verify that the parcel is in unincorporated Mercer County, where a county residential building permit is not required1.
  1. Ask the Mercer County Commission or County Clerk whether any zoning, floodplain, setback, or county-road requirement applies to the parcel34.
  1. Arrange the septic site evaluation early because 0% of county soils are rated without severe limits for a conventional drain field17.
  1. Submit project information to Missouri DHSS for an application number, then wait for DHSS to issue the construction permit or confirm an exemption before installing or repairing the onsite system756. If you plan to install the system yourself, ask DHSS whether that is allowed and what permit is required86.
  1. If subdividing or developing land for onsite wastewater, obtain Missouri DNR approval and comply with the state residential-development and onsite-sewage rules19.
  1. If the driveway enters a state highway, obtain MoDOT's right-of-way permit before construction14.
  1. Use a properly permitted Missouri contractor for regulated private-well construction or pump work20.

What should you check before buying land in Mercer County?

Start with wastewater feasibility: 0% of Mercer County soils are rated without severe limits for a conventional drain field, while 64.7% of county land has a slope of 15% or less1721. Check flood maps and ask the County Commission whether the parcel is subject to a local floodplain process, because Missouri's floodplain requirements depend on both a designated hazard area and a participating jurisdiction223. Confirm legal road access, and obtain a state permit if a new or modified driveway enters MoDOT right-of-way14. Mercer County is very rural, with 7.6 people per square mile, and the nearest city of 100,000 or more is about 79 miles from the county center2324. The effective property-tax rate is about 0.9%, with a median annual property-tax bill of $9052526.

Watch-outs

  • County zoning, RV occupancy, tiny-home occupancy, setbacks, and minimum dwelling size remain unconfirmed; ask the Mercer County Commission or County Clerk before committing to a use or site plan234.
  • All Mercer County soils are rated severely limited for a conventional septic drain field, so site evaluation may materially change the system design and budget17.
  • Missouri's onsite-sewage application fees are temporarily suspended, so confirm the current charge with DHSS when requesting an application number166.

Sources

  1. Missouri Department of Economic Development - County Building Codes dataset (data.mo.gov) (2026 county census)
  2. (2026 county census)
  3. Mercer County Presiding Commissioner (mocounties.com)
  4. Mercer County Clerk (mocounties.com)
  5. OWTS Construction Permit Process, quoted and re-checked
  6. Missouri DHSS Onsite Wastewater Treatment Program (health.mo.gov)
  7. OWTS Construction Permit Process | Missouri Department of Health and Senior Services, quoted and re-checked
  8. health.mo.gov, quoted and re-checked
  9. health.mo.gov, quoted and re-checked
  10. RSMo Section 64.170 (Missouri statewide rule), quoted and re-checked
  11. RSMo § 64.170 — County commissions control construction and issue building permits (Missouri statewide rule), quoted and re-checked
  12. RSMo Section 64.003 — Farm buildings and farm structures (Missouri statewide rule), quoted and re-checked
  13. OWTS Construction Permit Process, quoted and re-checked
  14. Permits | Missouri Department of Transportation (Missouri statewide rule), quoted and re-checked
  15. RSMo § 64.090 — Planning and zoning powers of county commission (Missouri statewide rule), quoted and re-checked
  16. OWTS Construction Permit Process — Temporary Permit Fee Suspension, quoted and re-checked
  17. 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
  18. health.mo.gov (Missouri statewide rule), quoted and re-checked
  19. Resources | Missouri Department of Health and Senior Services, quoted and re-checked
  20. Well and Pump Installation Contractor Permitting (Missouri statewide rule), quoted and re-checked
  21. Share of land at 15% slope or less: Bolthole Index county data
  22. Laws and Regulations That Might Affect You if You Mine Sand or Gravel From Missouri Streams (Missouri statewide rule), quoted and re-checked
  23. Population density: Bolthole Index county data
  24. Straight-line distance from the county center to the nearest city of 100,000+ people: Bolthole Index county data
  25. Effective property tax rate: Bolthole Index county data
  26. Median property tax bill: Bolthole Index county data

Written October 7, 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 5 of its 6 neighbors, Mercer County requires no county building permit for a home.

RuleMercer CountyGrundy CountyHarrison CountyPutnam CountySullivan CountyDaviess CountyLivingston County
Building permitNot requiredNot requiredNot requiredNot requiredNot requiredNot requiredRequired
County zoningNot publishedNot publishedNot publishedNot publishedNot publishedNoYes
Septic permitsMO Dept. of Health & Senior ServicesMO DHSS Onsite Wastewater Treatment ProgramDHSSDHSSMO Dept. of Health & Senior ServicesCounty Health Dept.DHSS

County locator

Mercer County in Missouri

75
County map
Mercer County highlighted among the Missouri counties · colored by Index score

How Mercer County scores

Seclusion79100% ev.
Self-Sufficiency58100% ev.
Admin Boringness7868% ev.
Durability49100% ev.
Property Autonomy47100% ev.
Carry Cost82100% ev.

Evidence strength: 95%. This reports direct-source completeness and fallback use; it is separate from the score and is not a confidence interval. How it works →

$143kTypical home
0.9%Property tax
$3,903Land / acre
38.7"Annual rain
6% of yrsSevere drought
10.3 / yr (+8.4)Mid-century 100°F days
17.2 daysMid-century dry spell
1.92" (+5.2%)Mid-century 1-day rain
1.82×Wildfire change factor
100%Forward climate coverage
$1,776Home insurance / yr
5.7% / yrInsurance growth
1.46%Nonrenewal rate
county median (2+ published ZIPs)Insurance basis
3,808People within 30 min
1,446,555People within 2 hr
6,084Radius comparison (15 mi)
7.6People / sq mi
0.2%Federal land
64.7%Land at 15% slope or less
0%Soils rated "not limited" for septic (strict USDA rating)
0 acWorkable land screen
29.9%Wooded land
44 tonsBiomass / forest ac
51.5°FAvg temp

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Cities and towns in Mercer County

Inside a city or town, that city usually issues building permits and sets zoning; the county’s rules above cover unincorporated land. Septic, wells and floodplain rules usually stay with the county or state everywhere.

Harrison Township · Lindley Township · Madison Township · Marion Township · Medicine Township · Town of Mercer · Morgan Township · Princeton · Ravanna Township · Somerset Township · Town of South Lineville · 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 permitNot required

    Missouri has no statewide residential building code and the state's official county building-code dataset lists no residential or commercial code adopted for Mercer County; as a non-charter rural county it generally cannot require a building permit. Corroborated by the state County Building Codes dataset (data.mo.gov iq7s-izvt, 2021): no county residential building code adopted.

    Missouri Department of Economic Development - County Building Codes dataset (data.mo.gov) ↗Scouted from the county site, not yet independently re-checked

Missouri rules that apply here

  • Owner-builder exemptionConditional

    A homeowner installing the homeowner's own onsite wastewater treatment system in Missouri, including Mercer County.

    • The official FAQ states that homeowners may install their own system in some instances.
    • The homeowner must check with the local permitting authority.
    • A construction permit may still be required.
    • The state strongly encourages using a registered installer.
    “In some instances, homeowners may install their own system.”
  • Building code adoptedPartial

    Missouri statewide legal framework for building-code adoption by counties and other communities; the statutes authorize local adoption rather than establishing one uniformly adopted statewide building code.

    • County authority under RSMo 64.170 applies to counties of the first and second classification.
    • A county that had not adopted a building code before August 28, 2001 must obtain voter approval before adopting under RSMo 64.170 to 64.200.
    • The adoption vote is limited to voters in the affected area; a code affecting a county is not voted on by citizens of incorporated territory.
    • A county adopting under RSMo 64.180 must use a current nationally recognized building code edition from calendar year 1999 or later, as amended.
    • A county building ordinance may not conflict with liquefied petroleum gas installation requirements governed by RSMo 323.020.
    • A community may incorporate a code by reference only if it otherwise has legal power to adopt the ordinance.
    • A code incorporated by reference must be filed with the community clerk and available for public inspection for 90 days before adoption.
    • An ordinance adopting a code by reference must state the penalty separately rather than incorporate the penalty by reference.
    • RSMo 67.280 defines community to include any county, fire protection district, or municipality, and municipality to include an incorporated city, town, or village.
    “Because fire and building codes are adopted at the local level in Missouri”
    2 more reviewed findings on this topic
  • Zoning districtsPartial

    Missouri statutory authority for counties to create zoning districts in unincorporated territory; this does not establish or publish the actual zoning districts for any particular county.

    • The statute applies to unincorporated territory of counties subject to sections 64.211 to 64.295.
    • Actual district boundaries, regulations, and maps depend on county adoption and are not supplied by this statewide statute.
    • District regulations must be uniform for each class or kind of building or land use within each district, although regulations may differ between districts.
    • The regulations must be made in accordance with a comprehensive plan.
    “the unincorporated territory may be divided into districts of such number, shape and area as may be deemed best suited”
  • Minimum lot sizeNone

    Minimum lot size for onsite wastewater treatment systems in Mercer County where Missouri state onsite laws apply.

    • The statement applies only where the state onsite laws apply.
    • A county with a wastewater ordinance may impose restrictions.
    • Some subdivisions may have a minimum approved lot size for onsite systems.
    • DNR provides written approval for the method of wastewater treatment for some subdivisions.
    • Lagoons typically require more land because of greater setback requirements.
    “Where the state onsite laws apply, it does not set a minimum lot size.”
  • Who permits septicState (with conditions)

    Onsite wastewater permitting for Mercer County, Missouri, including single-family residential systems and other systems within DHSS jurisdiction.

    • A construction permit is required before installing or repairing most onsite wastewater treatment systems.
    • Some single-family residential lots may be exempt from permitting.
    • Mercer County is identified in the Missouri DHSS permitting table with Agency: DHSS and Authority Type: DHSS.
    • DHSS regulations cover single-family residential systems, including lagoons, and onsite or cluster systems treating domestic wastewater flows of 3,000 gallons per day or less that disperse wastewater through soil treatment or absorption systems.
    • The Missouri Department of Natural Resources regulates lagoons serving anything other than single-family residences, systems discharging into surface waters, systems treating flows greater than 3,000 gallons per day and dispersing through soil treatment or absorption systems, and industrial non-domestic wastewater systems.
    • DNR approval is required for subdivisions, mobile home parks, and campgrounds if onsite wastewater treatment systems are planned.
    • Effective August 28, 2026, application fees for onsite sewage disposal system construction, modifications, and repairs are temporarily suspended.

    domestic wastewater flow threshold: <= 3000 gallons per day (Systems above this threshold are regulated by DNR when they disperse wastewater through soil treatment or absorption systems.) · permit-fee suspension effective date: 2026-08-28 (Temporary suspension under RSMo 701.046 changes.)

    “Mercer [...] State Administered – Contact DHSS Onsite Wastewater Program”
    2 more reviewed findings on this topic
    • Mixed — Missouri wastewater treatment systems, including domestic onsite systems, larger-flow systems, direct discharges, lagoons, subdivisions, and industrial wastewater.
      “In Missouri, different state and local agencies are responsible for regulating wastewater treatment systems.”
    • Mixed (with conditions) — Onsite wastewater treatment systems statewide in Missouri.
      “DHSS OWTS permitting falls under one of three authority types: DHSS Onsite Program, Local Authority (contract), or Local Authority via Ordinance. The application process varies by permitting authority.”
  • Septic permitLimited

    Installation or repair of onsite wastewater treatment systems in Missouri, including work in Mercer County subject to the applicable permitting authority.

    • A permit is required before installing or repairing most OWTS.
    • Some single-family residential lots may be exempt from permitting.
    • The first step is to determine the agency with permitting authority where the work occurs.
    • Work should not begin until a permit has been issued or an exemption has been confirmed by the applicable authority.
    • Effective August 28, 2026, application fees for onsite sewage disposal system construction, modifications, and repairs are temporarily suspended pending new standards.
    • Lagoons serving anything other than a single-family residence are under DNR jurisdiction.
    • DHSS regulations cover single-family residential systems including lagoons and onsite or cluster systems treating domestic wastewater flows of 3,000 gallons per day or less that disperse through soil treatment or absorption systems.
    • DNR must approve subdivisions, mobile-home parks, and campgrounds where OWTS use is planned.

    DHSS domestic wastewater flow threshold: <= 3000 gallons per day (System must disperse wastewater through soil treatment/absorption systems.)

    “A construction permit is required before installing or repairing most onsite wastewater treatment systems (OWTS). Some single family residential lots may be exempt from permitting. The first step of the permitting process is to determine the agency that has permitting authority where the work is being done.”
    4 more reviewed findings on this topic
    • Required — Onsite wastewater system installation or repair in Mercer County where Missouri state onsite-wastewater standards apply.
      “A construction permit is required to install or repair an onsite system on any residential property less than three acres. (This exemption does not apply in some counties; check with the county authority.) Regardless of the size of the property, a permit is necessary for all other onsite systems that serve non-residential structures.”
    • Required — Installing or repairing most onsite wastewater treatment systems in Missouri, including residential systems subject to state permitting.
      “A construction permit is required before installing or repairing most onsite wastewater treatment systems (OWTS). Some single family residential lots may be exempt from permitting.”
    • Required — Installing or repairing most onsite wastewater treatment systems statewide in Missouri.
      “A construction permit is required before installing or repairing most onsite wastewater treatment systems (OWTS). Some single family residential lots may be exempt from permitting.”
    • Required — Proposed campgrounds, mobile home parks, and subdivisions planning to use onsite wastewater treatment systems anywhere in Missouri.
      “DNR must approve subdivisions, mobile home parks and campgrounds if the use of OWTS is planned.”
  • Septic inspectionLimited

    Inspection or evaluation of existing onsite wastewater systems in connection with Missouri real-estate transfers.

    • Local public health agencies generally no longer inspect existing systems for real-estate transfers.
    • A private licensed inspector may perform an inspection or evaluation.
    • A lender, buyer, or other transaction participant may require an assessment.
    • Some local standards may be more stringent than state regulations.
    • Inspections and evaluations are distinct; an inspection includes a hydraulic test, while an evaluation does not.
    “For the most part, local public health agencies no longer inspect existing systems related to real estate transfer. The help of a licensed inspector can be obtained to check the condition of the system.”
    One more reviewed finding on this topic
    • Limited — Inspections of existing onsite sewage systems in connection with property sales statewide in Missouri.
      “Missouri Department of Health and Senior Services' (DHSS) rules governing onsite sewage systems cover minimum construction requirements, system inspections at the time of property sales, and requirements for percolation testers and soil evaluators.”
  • Off-grid sanitationLimited

    Off-grid domestic wastewater treatment using onsite wastewater treatment systems where central sewer service is unavailable.

    • Onsite systems treat and dispose of domestic sewage on the property where generated.
    • A construction permit is generally required, including for residential property less than three acres, subject to county-specific exceptions.
    • Wastewater may not be discharged into a road ditch or onto the ground.
    • Local permitting authorities may impose additional requirements.

    residential lot threshold: < 3 acres (The exemption does not apply in some counties.)

    “Onsite wastewater treatment systems are sometimes referred to as "septic systems." These systems treat and dispose of domestic sewage on the property where it is generated.”
    One more reviewed finding on this topic
    • Allowed (with conditions) — Use of onsite wastewater treatment systems as off-grid sanitation where central sewer service is unavailable in Missouri.
      “In Missouri, where central sewer service is not available, homeowners and small business owners use various types of onsite wastewater treatment systems (OWTS).”
  • Well permitLimited

    Construction or alteration of a public well serving a Missouri public water system.

    • Public water systems must receive written approval from the Missouri Department of Natural Resources Public Drinking Water Branch before constructing or altering a public well.
    • The requirement does not apply when the system meets the charitable-and-benevolent-organization exemptions in section 640.116, RSMo.
    • Anyone proposing to install a public well must contact the department’s regional office for a well-site survey.
    • The survey addresses minimum isolation or setback distances from known or potential contaminant sources, including septic tanks, sanitary sewer lines, and landfills.
    • Before applying for construction authorization, the public water system must obtain an estimated casing-depth letter from the Missouri Geological Survey Water Resources Center.
    • There is no fee for the well-site-survey and estimated-casing-depth-letter services.
    • Failure to obtain construction authorization may result in approval delays and possibly require the owner to properly plug the well and drill a new one according to 10 CSR 60-3.

    public water system threshold: at least 15 service connections or regularly serves an average of at least 25 individuals daily, at least 60 days per calendar year

    “Public water systems must receive written approval from the PDWB before constructing or altering a public well”
    2 more reviewed findings on this topic
    • Required — A person or contractor conducting regulated work to drill, construct, repair, reconstruct, plug, or install pumps or pumping equipment in a water well, heat-pump well, monitoring well, or related well in Missouri.
      “A non-restricted permit is required to drill, construct, repair, reconstruct, plug, or install pumps or pumping equipment in a well.”
    • Limited — Construction or repair of water wells, installation or replacement of pumps, and associated plumbing and electrical work in Missouri.
      “A non-restricted water well installation permit is required to construct or repair a water well in Missouri.”
  • Agricultural exemptionAvailable (with conditions)

    Farm buildings and farm structures used for agricultural purposes under the county building and land-use restriction provisions of RSMo sections 64.800 to 64.905.

    • The exemption does not apply within incorporated portions of counties.
    • The exemption applies to raising crops, livestock, orchards, or forestry and to specified rice-farming or flood-irrigation impoundments.
    • For farm buildings or farm structures, the area must not be within the area shown on the flood hazard area map.
    • The statute preserves the validity of county ordinances or orders adopted before March 4, 1991.
    • Other laws and local requirements may still apply.

    rice-farming or flood-irrigation berm height: <= 18 inches (small berms placed around a field to hold water for growing rice or flood irrigation)

    “This section shall not apply to the erection, maintenance, repair, alteration or extension of farm buildings or farm structures used for such purposes in an area not within the area shown on the flood hazard area map.”
    4 more reviewed findings on this topic
    • Available (with conditions) — Erection, maintenance, repair, alteration, or extension of farm buildings or farm structures as against county fire-protection or fire-prevention ordinances.
      “Notwithstanding any provision of law to the contrary, no fire protection or fire prevention ordinance adopted by any county in this state shall be exercised so as to impose regulations or to require permits with respect to the erection, maintenance, repair, alteration, or extension of farm buildings or farm structures.”
    • Available (with conditions) — Erection, maintenance, repair, alteration, or extension of farm buildings or farm structures used for agricultural purposes under RSMo section 64.890, outside incorporated portions of counties and outside areas shown on flood hazard area maps.
      “This section shall not apply to the erection, maintenance, repair, alteration or extension of farm buildings or farm structures used for such purposes [...]”
    • Available (with conditions) — Farm buildings and farm structures statewide, with respect to county fire-protection and fire-prevention ordinances.
      “no fire protection or fire prevention ordinance adopted by any county in this state shall be exercised so as to impose regulations or to require permits [...]”
    • Available — Erection, maintenance, repair, alteration, or extension of farm buildings or farm structures with respect to county fire-protection or fire-prevention ordinances.
      “Notwithstanding any provision of law to the contrary, no fire protection or fire prevention ordinance adopted by any county in this state shall be exercised so as to impose regulations or to require permits with respect to the erection, maintenance, repair, alteration, or extension of farm buildings or farm structures.”
  • Subdividing landLimited

    Subdivision plats in the unincorporated areas of counties covered by RSMo section 64.070 after the county commission adopts subdivision regulations.

    • The county commission must first adopt subdivision regulations.
    • The plat must first be submitted to the planning commission.
    • If the county planning commission does not report upon the plat within thirty days, it may then be deemed approved.
    • If amended or rejected by the planning commission, the action may be overruled and the plat approved only by the county commission, with the reasons for overruling spread upon the county commission minutes.
    • The recorder of deeds may not record the plat until receiving a certificate of authority from the county zoning enforcement officer.
    • The statute also permits a county planning commission, upon written request of an incorporated area's legislative body where there is no municipal planning commission, to pass upon subdivision plats within that incorporated area; those plats are subject to county planning commission rules and approval procedures.

    planning commission reporting period: 30 days (If no report is made, the plat may then be deemed approved.)

    “After the county commission shall have adopted such subdivision regulations, no plat of a subdivision of land within the unincorporated area of such county [...]”
    2 more reviewed findings on this topic
    • Regulated (with conditions) — Subdivision or development of property in Missouri, including Mercer County, when onsite wastewater is involved.
      “Anyone subdividing or developing property must comply with DNR residential development regulations as well as the onsite sewage law.”
    • Limited — Subdivision regulations adopted by Missouri cities, towns, or villages under RSMo section 89.410.
      “The planning commission shall recommend and the council may by ordinance adopt regulations governing the subdivision of land within its jurisdiction.”
  • Driveway accessRequired

    Construction or modification of driveways within MoDOT right-of-way statewide.

    • A permit is required for construction of driveways and modifications to existing driveways on MoDOT right-of-way.
    • An initial online request must be submitted for each planned listed activity.
    • Engineered plans, traffic studies, hydraulic analysis, traffic-control plans, surety deposits, or performance bonds may be required depending on the work.
    • The rule does not establish a permit requirement for driveways outside MoDOT right-of-way.
    “We require you to obtain a permit to work on MoDOT's Right of Way for: Construction of driveways”
  • Building in a floodplainLimited

    Projects including mining, dredging, building construction, and other dirt-moving activities in designated flood hazard areas within participating Missouri jurisdictions.

    • The source describes local county or city flood damage reduction ordinances rather than one uniform statewide ordinance.
    • The project must be within a participating jurisdiction.
    • The project must be within a designated flood hazard area.
    • The cited rule does not apply if either condition is absent.
    • Covered projects must not raise flood heights.
    “Some jurisdictions (for example, county, city) require any projects in certain floodplains do not raise flood heights.”
    One more reviewed finding on this topic
    • Required — All development in a Missouri floodplain, administered through the applicable community floodplain permitting process.
      “Regardless, some type of permit MUST be issued for ALL development in the floodplain.”
  • Permit feesPublished (with conditions)

    Missouri Department of Natural Resources air construction permits statewide.

    • Fees apply to air construction permits, not to every Missouri building or land-use permit.
    • Construction permit fees include a filing fee and an hourly processing fee.
    • The filing fee depends on the type of construction permit.
    • The listed fees are effective January 1, 2026.
    • Fees applicable until December 31, 2025 are available on the Air Construction Permit Fees white sheet.
    • A convenience fee is charged for electronic payment.

    portable source relocation filing fee: 300 USD · minor permit filing fee: 300 USD · minor permit processing fee: per 100 USD (hour) · general permit filing fee: 700 USD · new source review filing fee: 6000 USD (plus $100 per hour processing fee) · prevention of significant deterioration filing fee: 6000 USD (plus $100 per hour processing fee) · hazardous air pollutant filing fee: 6000 USD (plus $100 per hour processing fee) · temporary or pilot filing fee: 250 USD (plus $100 per hour processing fee)

    “Construction permit fees include a filing fee and an hourly processing fee. The filing fee is dependent on the type of construction permit.”
    2 more reviewed findings on this topic
    • Published (with conditions) — Missouri onsite sewage disposal system construction, modification, and repair application fees applicable to Mercer County when DHSS rules govern.
      “Effective August 28, 2026, due to changes to RSMo 701.046, the application fees associated with on-site sewage disposal system construction, modifications, and repairs will be temporarily suspended. 701.046 was changed to take out the $90 permit fee and authorizes the Department of Health and Senior Services to set reasonable fees—effectively placing current fees on hold until the new standards take effect.”
    • Published (with conditions) — Missouri onsite wastewater treatment system construction, modification, and repair application fees administered under the statewide DHSS OWTS program.
      “Effective August 28, 2026, [...] the application fees associated with on-site sewage disposal system construction, modifications, and repairs will be temporarily suspended.”
  • Permit processPublished (with conditions)

    Installation or repair of most onsite wastewater treatment systems in Missouri.

    • Some single-family residential lots may be exempt from permitting.
    • The applicant must determine which agency has permitting authority where the work is being done.
    • DHSS permitting may be administered by the DHSS Onsite Program, a local authority under contract, or a local authority via ordinance.
    • Work should not begin until a permit has been issued or an exemption has been confirmed.
    • DHSS regulates single-family residential systems and onsite or cluster systems treating domestic wastewater flows of 3,000 gallons per day or less that disperse wastewater through soil treatment or absorption systems.
    • DNR regulates other systems, including non-single-family lagoons, systems discharging to surface waters, systems over 3,000 gallons per day, and industrial wastewater systems.
    • DNR must approve subdivisions, mobile home parks, and campgrounds if OWTS use is planned.

    domestic wastewater flow threshold: <= 3000 gallons per day (Systems above this threshold are regulated by DNR when they disperse wastewater through soil treatment or absorption systems.)

    “A construction permit is required before installing or repairing most onsite wastewater treatment systems (OWTS). Some single family residential lots may be exempt from permitting.”
    3 more reviewed findings on this topic
    • Published (with conditions) — Missouri onsite wastewater treatment permitting, including applicable systems in Mercer County.
      “DHSS OWTS permitting falls under one of three authority types: DHSS Onsite Program, Local Authority (contract), or Local Authority via Ordinance. The application process varies by permitting authority. Work should not begin until a permit has been issued or an exemption to permitting has been confirmed by the appropriate permitting authority.”
    • Partial — State-administered OWTS construction-permit process applicable where DHSS is the permitting authority.
      “DHSS OWTS permitting falls under one of three authority types: DHSS Onsite Program, Local Authority (contract), or Local Authority via Ordinance. The application process varies by permitting authority. Work should not begin until a permit has been issued or an exemption to permitting has been confirmed by the appropriate permitting authority.”
    • Published (with conditions) — Permit applications for work on Missouri Department of Transportation right-of-way statewide.
      “Contact the Traffic Specialist a minimum of 48 hours prior to beginning work and for all necessary inspections.”
  • county zoning authorityLimited

    Missouri county zoning authority over unincorporated land.

    • RSMo § 64.850 applies to counties of the first class without a charter and counties of the second, third, or fourth class.
    • RSMo § 64.620 applies to counties of the second or third class to which §§ 64.510–64.690 apply.
    • Adoption under §§ 64.510–64.690 requires approval by vote of the people under § 64.530.
    • The authority applies in unincorporated portions and not incorporated portions.
    • The regulations must be in accordance with a comprehensive plan.
    • Under § 64.090, the zoning power does not apply to raising crops, livestock, orchards, or forestry; seasonal or temporary rice-farming or flood-irrigation impoundments; specified farm structures outside mapped flood-hazard areas; or underground mining entered through shafts outside mapped flood-hazard areas.
    • Existing lawful uses and specified public-utility services are protected under the cited statutory schemes.
    “the county commission of any county of the first class not having a charter form of government, or of any county of the second, third or fourth class may, after approval by vote of the people as provided in section 64.845, regulate and restrict, by order of record, in the unincorporated portions of the county, the height, number of stories, and size of buildings, the percentage of lots that may be occupied, the size of yards, courts and other open spaces, the density of population, the location and use of buildings, structures and land for trade, industry, residence or other purposes.”
    2 more reviewed findings on this topic
  • county building authorityLimited

    County authority to regulate residential construction and issue building permits in unincorporated areas of Missouri.

    • The authority under sections 64.170 to 64.200 applies to counties of the first and second classification.
    • A county that had not adopted a building code before August 28, 2001, must obtain voter approval before adopting one under those sections.
    • Only voters in the area affected by the proposed code may vote; incorporated-territory citizens cannot vote on a code affecting a county.
    • The county commission must hold at least three public hearings and provide the statutory newspaper publication and county posting notices before adoption.
    • Regulations adopted under section 64.180 apply to unincorporated territory, except as otherwise provided.
    • Adopted or amended codes after August 28, 2001, must use a current, calendar year 1999 or later edition of a nationally recognized building code, as amended.
    • A county building ordinance may not conflict with liquefied petroleum gas installations governed by section 323.020.

    public hearings before adoption: >= 3 hearings minimum (Section 64.180(3)) · newspaper notice: >= 15 days (Notice of hearing time and place must be published in at least two newspapers having general circulation within the county) · posted notice: >= 15 days (Notice must be posted in four conspicuous places in the county) · minimum nationally recognized building-code edition: >= calendar year 1999 edition year (Applies after August 28, 2001, under section 64.180)

    “The regulations adopted shall be applicable to the unincorporated territory of the county, except as otherwise provided herein”
    2 more reviewed findings on this topic
    • Limited — County regulation of construction and issuance of building permits for buildings, including residential construction, in Missouri counties, with the practical focus on county-controlled areas outside incorporated territory.
      “the county commission in all counties of the first and second classification [...] is for this purpose empowered [...] to adopt [...] regulations to control the construction”
    • Limited — Missouri counties' authority to require permits and regulate residential construction in unincorporated areas.
      “Before the adoption of such code of regulations, the county commission shall hold at least three public hearings thereon”

Still unanswered

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

  • Inspections — Building inspections for residential construction in unincorporated Mercer County.
  • Certificate of occupancy — Certificates of occupancy for residences in unincorporated Mercer County.
  • County-wide zoning — County zoning in Mercer County, including unincorporated areas.
  • Local zoning — Zoning administered by local governments within Mercer County.
  • Minimum dwelling size — Minimum dwelling size in unincorporated Mercer County.
10 more unanswered
  • Setbacks
  • Lot coverage
  • Building height
  • Living in an RV
  • Camping on your land
  • Tiny homes
  • Manufactured homes
  • Accessory dwellings
  • Mandatory utility hookup
  • Short-term rentals

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, Missouri

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

Mercer County scores 75/100 on the Bolthole Index, a strong county profile. Its strengths: manageable long-term carry cost and sparse surroundings — about 3,808 people within a 30-minute drive.

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

Mercer County does not require a county building permit for a home in unincorporated areas. Onsite septic is permitted by Missouri Department of Health and Senior Services, Onsite Wastewater Treatment Program. 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, Missouri?

Land in Mercer County runs about $3,903 per acre, based on the latest county data.

What is the water situation in Mercer County?

Mercer County gets about 38.7" of rain a year, with severe drought in roughly 6% of years.

How remote is Mercer County?

A representative private-land location has about 3,808 people within a 30-minute drive and 1,446,555 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 Missouri

Compare side-by-side →See all 115 Missouri counties ranked →