Bolthole Index

Mercer County, Illinois

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

65Index Score / 100
#37 of 102 in Illinois

Unincorporated Mercer County, Illinois requires a building permit from Mercer County Zoning and is subject to county zoning12. Inside municipal limits, ask the city or village hall about building permits and zoning approval3. The Mercer County Health Department handles septic permits countywide under Illinois Department of Public Health regulation; surface-discharging systems also need an Illinois EPA discharge permit45.

At a glance

Building permit
Required through Mercer County Zoning outside municipalities; ask the city or village hall inside municipal limits13
Building permit fee
$25 application fee plus $5 per $1,000 of improvement cost6
Zoning
County zoning applies outside municipalities; contact city or village hall inside municipal limits73
Septic permit
Construction or repair requires Mercer County Health Department approval under state sewage rules45
RV living
R-3 conditional-use campgrounds allow no more than 30 days per calendar year; other private-land occupancy is unconfirmed8
Manufactured home
District-specific permits, occupancy limits and minimum living areas apply9
Agricultural use
Exempt from the zoning ordinance's general permit and certificate provisions10
Private well
A permit is required before construction, modification or sealing11

Who to call

Building permits

Mercer County Zoning

Mercer County building permits, zoning applications, zoning questions and certificates of occupancy

309-525-3799

zoning@mercercountyil.org

100 SE 3rd St Aledo, IL 61231

Septic permits

Mercer County Health Department

Permits to construct or repair onsite wastewater disposal systems in Mercer County

(309) 582-3759

305 NW 7th Street Aledo, Illinois 61231

Contact details are copied from each office’s official page and were checked against it on October 12, 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, Illinois?

Unincorporated Mercer County requires a building permit from Mercer County Zoning; ask the office which projects and exemptions apply112. Inside Aledo, the city handles building permits, including an all-inclusive permit, construction drawings and a survey for new homes13. Septic permits remain with the Mercer County Health Department countywide under state regulation45. County building-permit applications must show lot dimensions and proposed structure locations14. The county building-permit fee is $25 plus $5 per $1,000 of improvement cost, with a separate $25-per-foot tower or turbine charge6. Agricultural uses are exempt from the county zoning ordinance's general permit and certificate provisions, but applicable septic and state rules still apply10.

Who issues Mercer County building permits, and how do you reach them?

Mercer County Zoning handles county building-permit and zoning applications at 100 SE 3rd St, Aledo, IL 6123115. Call 309-525-3799 or email zoning@mercercountyil.org; the part-time office asks callers to allow up to 48 hours on weekdays for a response15. Applications may be emailed, but fees must be mailed, and the office mails the building permit after payment arrives15. Illinois statewide baseline building-code requirements took effect in 2025; ask the permitting jurisdiction which local amendments and code apply16. The Illinois Energy Conservation Code covers new buildings with county or municipal building-permit applications, subject to statutory exemptions; additions and repairs are covered only in the affected portions17. We could not confirm Mercer County's inspection schedule or full certificate-of-occupancy requirements; ask Mercer County Zoning15.

Does Mercer County, Illinois have zoning?

Mercer County zoning districts apply outside incorporated municipalities; for land inside municipal limits, contact the city or village hall27. Matherville has its own village zoning regulations18. Private septic systems inside Matherville still go through the Mercer County Health Department19. Complete county zoning applications must reach the zoning officer at least 30 days before the zoning-board meeting; zoning changes involve notice, zoning-board review and County Board action1420. The first land split may be any acreage without a subdivision plat; after that, parcels under 5 acres require a plat, with a $300 platting-officer fee2122. Ask Mercer County Zoning about rezoning separately from platting; the county publishes a separate acreage-based rezoning statement22. Obtain the parcel's district-specific lot, setback and height rules before designing a home2324.

How do septic permits work in Mercer County?

The Mercer County Health Department handles septic permits countywide under Illinois Department of Public Health regulation4. Construction or repair of an onsite wastewater system requires a septic permit5. Arrange an onsite soil evaluation with at least 3 borings by a certified soil classifier, protect the system area from compaction, and contact a licensed Mercer County private sewage disposal contractor unless homeowner installation applies2526. Submit the application, soil report and fee to the health department; contractor installation costs $200 and homeowner installation costs $600, and the septic permit lasts 1 year25. Surface-discharging systems also require an Illinois EPA NPDES discharge permit5. About 41.4% of county soils rate as free of severe limitations for a conventional drain field, so complete the soil evaluation before fixing the house site27.

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

Mercer County's R-3 Seasonal Home District allows travel trailers and camping trailers only as a conditional campground use, with occupancy limited to 30 days in a calendar year; mobile homes are excluded from that campground use8. That narrow rule does not establish that residential RV living is allowed on an ordinary private parcel, so ask Mercer County Zoning about the parcel's district, proposed use and length of stay15. We could not confirm a rule written specifically for tiny homes; ask Mercer County Zoning about the proposed dwelling15. Manufactured homes follow district-specific rules: R-3 seasonal homes and R-4 homes require individual building permits and at least 600 square feet, while specified AG-1 farm dwellings and hardship placements require conditional-use permits and at least 825 square feet9.

What are the steps to building a home in Mercer County?

  1. Establish whether the parcel is unincorporated or inside municipal limits, then ask Mercer County Zoning or the city or village hall for the applicable district23.
  2. Before buying a split parcel, ask Mercer County Zoning about subdivision platting and any separate rezoning requirement2122.
  3. Prepare lot dimensions and structure locations for a county building-permit application; zoning applications need at least 30 days before board review14.
  4. Arrange soil evaluation, then submit the septic application, soil report and fee to the Mercer County Health Department25.
  5. Apply for the building permit through the governing jurisdiction and confirm applicable codes, including energy requirements1317.
  6. Obtain an IDOT driveway permit before access work in a state-maintained road right-of-way28.

What should you check before buying land in Mercer County?

Before buying in Mercer County, establish the governing jurisdiction and zoning district with Mercer County Zoning or the applicable city or village hall23. Ask the zoning office about land-split platting and separate rezoning requirements rather than treating acreage alone as approval to build2122. Order the septic soil evaluation early: about 41.4% of county soils rate as free of severe limitations for a conventional drain field27. A new, modified or sealed private well needs a permit before work begins11. Mercer County's effective property-tax rate is about 1.9%, with a median annual bill near $2,7102930.

Watch-outs

  • Mercer County publishes building-permit fees and application details but does not define every type of covered work; ask Mercer County Zoning about the specific project before starting1215.
  • The 30-day RV limit applies specifically to conditional-use campgrounds in the R-3 district; long-term RV living on an ordinary private parcel and tiny-home occupancy remain unconfirmed815.
  • Gas and electric service cannot be turned on before a certificate of occupancy for buildings subject to that county rule31.

Sources

  1. Mercer County IL - Zoning Department (2026 county census)
  2. ZONING RESOLUTION, quoted and re-checked
  3. Zoning, quoted and re-checked
  4. Private Sewage Disposal | Illinois Department of Public Health, quoted and re-checked
  5. Onsite Wastewater Disposal Permit Application Instructions, quoted and re-checked
  6. Mercer County Zoning, quoted and re-checked
  7. Zoning, quoted and re-checked
  8. Mercer County Zoning Ordinance, quoted and re-checked
  9. ZONING RESOLUTION, quoted and re-checked
  10. ZONING RESOLUTION, Sections 15.5.01-15.5.05, quoted and re-checked
  11. 77 Ill. Admin. Code 920.130, Water Well Permit Requirements (Illinois statewide rule), quoted and re-checked
  12. Zoning, quoted and re-checked
  13. Aledo: Aledo City Code § 4-1-3, Permit, Plan and Survey Requirements (Mercer County), quoted and re-checked
  14. Mercer County Zoning, quoted and re-checked
  15. Mercer County Zoning (mercercountyil.org)
  16. Building Codes and Regulations, quoted and re-checked
  17. ilga.gov, quoted and re-checked
  18. Village of Matherville: Title 10 Zoning Regulations (Mercer County), quoted and re-checked
  19. Village of Matherville: Private Sewage Disposal (Mercer County), quoted and re-checked
  20. Zoning | Mercer County, IL, quoted and re-checked
  21. Zoning | Mercer County, IL, quoted and re-checked
  22. Zoning, quoted and re-checked
  23. ilga.gov (Illinois statewide rule), quoted and re-checked
  24. 55 ILCS 5/5-12001 — Authority to regulate and restrict location and use of structures (Illinois statewide rule), quoted and re-checked
  25. Onsite Wastewater Disposal Permit Application Instructions, quoted and re-checked
  26. Onsite Wastewater Disposal Permit Application Instructions, quoted and re-checked
  27. 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
  28. Highway Permits (Illinois statewide rule), quoted and re-checked
  29. Effective property tax rate: Bolthole Index county data
  30. Median property tax bill: Bolthole Index county data
  31. ZONING RESOLUTION, Sections 15.5.01-15.5.05, quoted and re-checked

Written October 12, 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 all 5 of the neighbors with published rules, Mercer County has countywide zoning.

RuleMercer CountyWarren CountyHenderson CountyRock Island CountyHenry CountyKnox CountyStark County
Building permitRequiredRequiredLimitedRequiredRequiredRequiredRequired
County zoningYesYesNot publishedYesYesYesYes
Septic permitsCounty Health Dept.County Health Dept.County Health Dept.County Health Dept.County Health Dept.County Health Dept.Henry & Stark County Health Dept.

County locator

Mercer County in Illinois

65
County map
Mercer County highlighted among the Illinois counties · colored by Index score

How Mercer County scores

Seclusion66100% ev.
Self-Sufficiency54100% ev.
Admin Boringness4390% ev.
Durability72100% ev.
Property Autonomy42100% ev.
Carry Cost56100% 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 →

$173kTypical home
1.9%Property tax
$9,250Land / acre
37.8"Annual rain
4.1% of yrsSevere drought
6.6 / yr (+6.1)Mid-century 100°F days
15 daysMid-century dry spell
1.89" (+8.2%)Mid-century 1-day rain
1.77×Wildfire change factor
100%Forward climate coverage
$1,480Home insurance / yr
4.2% / yrInsurance growth
1.13%Nonrenewal rate
county median (2+ published ZIPs)Insurance basis
6,684People within 30 min
1,447,405People within 2 hr
32,378Radius comparison (15 mi)
27.6People / sq mi
1.3%Federal land
89%Land at 15% slope or less
41.4%Soils rated "not limited" for septic (strict USDA rating)
145,458 acWorkable land screen
11.8%Wooded land
50.2 tonsBiomass / forest ac
50.5°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.

Not yet researched: Abington Township · Duncan Township · Eliza Township · Greene Township · Village of Joy · Keithsburg · Keithsburg Township · Mercer Township · Millersburg Township · New Boston · New Boston Township · North Henderson Township · Village of North Henderson · Ohio Grove Township · Perryton Township · Preemption Township · Richland Grove Township · Rivoli Township · Village of Seaton · Village of Sherrard · Suez Township · Village of Viola · Village of Windsor

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

  • County-wide zoningPresent (with conditions)

    Mercer County Zoning/Nuisance administration and zoning applications in the county.

    • The county page states that property may be within city limits; in that situation, the page directs the applicant to contact the applicable city or village hall.
    • Zoning applications must be submitted to the zoning officer at least 30 days before a zoning board meeting.
    • The linked county zoning ordinance was identified but was not accessible for detailed district-level extraction.

    minimum application lead time: >= 30 days (before the zoning board meeting)

    “All Mercer County zoning is in our Property tax software, if you don't see zoning it could be because: Please make sure the TAX YEAR at the tops says (drop down box) 2023(payable 2024). or it could be in City Limits, you when then need to contact City or Village Hall of the Corporates area.”
    2 more reviewed findings on this topic
    • Present (with conditions) — County zoning and nuisance administration in Mercer County, subject to incorporated-area jurisdictional limits.
      “Mercer County ZONING / NUISANCE: Mercer County Zoning [...] All Mercer County zoning is in our Property tax software, if you don't see zoning it could be because: Please make sure the TAX YEAR at the tops says (drop down box) 2023(payable 2024). or it could be in City Limits, you when then need to contact City or Village Hall of the Corporates area.”
    • Present (with conditions) — Land outside incorporated municipalities in Mercer County
      “For the purposes of this Resolution, all land located outside of the Incorporated municipalities in Mercer County is hereby divided into the Following districts:”
  • Local zoningVaries (with conditions)

    Aggregate zoning jurisdiction across Mercer County, including county zoning and incorporated municipalities.

    • The county administers county zoning outside incorporated areas; the county page directs users to the applicable city or village hall for property within city limits.
    • County zoning applications may require zoning board and county board action.
    “Mercer County ZONING / NUISANCE: Mercer County Zoning [...] All Mercer County zoning is in our Property tax software, if you don't see zoning it could be because: Please make sure the TAX YEAR at the tops says (drop down box) 2023(payable 2024). or it could be in City Limits, you when then need to contact City or Village Hall of the Corporates area.”
    One more reviewed finding on this topic
    • Varies (with conditions) — Aggregate zoning conditions across Mercer County, including county zoning and incorporated municipalities.
      “All Mercer County zoning is in our Property tax software, if you don't see zoning it could be because: Please make sure the TAX YEAR at the tops says (drop down box) 2023(payable 2024). or it could be in City Limits, you when then need to contact City or Village Hall of the Corporates area.”
  • Living in an RVLimited

    Travel trailers and camping trailers in R-3 Seasonal Home District campgrounds in unincorporated Mercer County.

    • The use is a conditional use requiring a campground used for seasonal recreation and living purposes.
    • Travel trailers must be vehicles identified by the manufacturer as travel trailers, built on a chassis 8 feet or less wide and designed to move on highways.
    • Camping trailers must be canvas folding structures built on a wheeled chassis and designed to move on highways.
    • Mobile homes are excluded from this campground use.
    • Occupancy may not exceed 30 days in any calendar year; exceeding 30 days is a violation of the special use.
    • One all-year residence for the property owner or manager is permitted as an accessory use.

    maximum occupancy: <= 30 days per calendar year (Exceeding 30 days violates the special use)

    “Campgrounds used for seasonal recreation and living purposes. The tracts may have located on them structures of a seasonal, temporary, or movable nature, such as a tent, travel trailer (a vehicle identified by the manufacturer as a travel trailer, built on a chassis 8 feet or less wide and designed to move on the highways), camping trailer (a canvas folding structure built on a chassis with wheels and designed to move on the highways), but not mobile homes. Provided that the occupancy of any of the foregoing shall not be for a period of more than 30 days in any calendar year and the occupancy of any of the foregoing for a period of more than 30 days in any calendar year shall be a violation of the special use herein permitted. One all year residence for property owner and/or manager is permitted as an accessory use.”
  • Manufactured homesLimited

    Manufactured or mobile homes in unincorporated Mercer County

    • HUD-code homes may be located in R-4 with a building permit and minimum 600 square feet; R-3 permits seasonal occupancy with individual building permits and minimum 600 square feet; AG-1 farm dwellings require conditional-use permits and minimum 825 square feet; hardship temporary occupancy in AG-1, R-1, R-2, and R-3 requires individual conditional-use permits and minimum 825 square feet.
    • The ordinance excludes recreational vehicles and certain conditional-use areas from the manufactured-home ordinance.

    minimum living area: >= 600 square feet (R-4 mobile-home districts and R-3 seasonal-home districts) · minimum living area: >= 825 square feet (AG-1 farm dwellings, hardship temporary occupancy, and specified individual lots)

    “ZONED R-3 SUMMER HOME DISTRICTS FOR SEASONAL OCCUPANCY WITH INDIVIDUAL BUILDING PERMITS. MINIMUM LIVING AREA IS 600 SQUARE FEET”
  • Who permits septicMixed (with conditions)

    Private sewage disposal systems in Mercer County, with state regulation and Mercer County Health Department implementation.

    • IDPH states that it regulates private sewage disposal systems statewide.
    • Local health agencies may review construction plans by local ordinance or as an agent of IDPH.
    • Mercer County Health Department states that it conducts regulatory programs for private on-site wastewater systems under an IDPH Local Health Protection Grant.
    “As a certified health department, the Mercer County Health Department (MCHD), through a Local Health Protection Grant from the Illinois Department of Public Health (IDPH), conducts regulatory programs to help ensure safe food is served at local establishments, private on-site wastewater systems properly dispose sewage, and new and existing water wells provide safe drinking (potable) water.”
    2 more reviewed findings on this topic
    • County — Private on-site wastewater and septic regulatory administration in Mercer County.
      “conducts regulatory programs to help ensure [...] private on-site wastewater systems properly dispose sewage”
    • County — Private onsite wastewater and related environmental-health regulation in Mercer County
      “the Mercer County Health Department (MCHD) [...] conducts regulatory programs to help ensure [...] private on-site wastewater systems properly dispose sewage”
  • Septic permitRequired

    Construction or repair of an onsite wastewater disposal system in Mercer County.

    • An onsite soils evaluation is required.
    • At least three soil borings must be made by a certified soil classifier.
    • The proposed system area must be protected from compaction.
    • The applicant must contact a licensed Mercer County private sewage disposal system contractor.
    • The application must include the soil report and permit fee.
    • A surface-discharging system requires an EPA NPDES permit issued by IEPA.

    contractor permit fee: 200 USD (Reg. Contractor) · homeowner installation permit fee: 600 USD · permit validity: 1 year

    “This is the permit application to construct or repair an onsite wastewater disposal system in Mercer County.”
    2 more reviewed findings on this topic
    • Required — Construction or repair of an onsite wastewater disposal system in Mercer County.
      “This is the permit application to construct or repair an onsite wastewater disposal system in Mercer County. The following procedure shall be followed when submitting an application for approval.”
    • Required — Construction or repair of onsite wastewater disposal systems in Mercer County
      “This is the permit application to construct or repair an onsite wastewater disposal system in Mercer County. [...] $200 for contractors, Home owner installation $600. Permit is valid for 1 year.”
  • Mandatory utility hookupConditional

    Gas and electric utility service for buildings subject to the county Certificate of Occupancy rule

    • Utility service cannot be turned on before issuance of a Certificate of Occupancy; municipal utility service-connection construction is exempt from the zoning certificate/permit rule.
    “Utility service (i.e., gas and electric) will not be turned on prior to issuance of a Certificate of Occupancy.”
  • Agricultural exemptionAvailable (with conditions)

    Agricultural uses in unincorporated Mercer County

    • The zoning ordinance's general certificate provisions exempt any agricultural uses from permit or certificate requirements; other state, health, wastewater, and environmental rules may still apply.
    “No permit or certificate shall be required for: [...] Any agricultural uses.”
  • Subdividing landRegulated (with conditions)

    Subdivision and land splits in Mercer County

    • The county page states that the first split may be any acreage without a subdivision plat; after the first split, parcels under 5 acres require a subdivision plat.
    • The county page states that a surveyor prepares the plat and a platting officer fee is collected.

    platting officer fee: 300 USD · post-first-split threshold: < 5 acres (requires subdivision plat)

    “1st time split can be any acres without S/D plat. After 1st split anything <5 acres need a subdivision plat done.”
    One more reviewed finding on this topic
    • Regulated (with conditions) — Subdivision platting in Mercer County.
      “SUBDIVISION PLATTING * Platting Officer fee: $300.00 Collected by Mercer County zoning officer.”
  • Permit feesPublished (with conditions)

    Published Mercer County zoning and building-permit fees

    • Building-permit fees are $25 application plus $5 per $1,000 of improvement cost and $25 per foot for towers/turbines.
    • Zoning-change applications list a $200 nonrefundable fee; conditional-use applications list $200 first-time and $150 annual renewal; variance applications list $125; subdivision platting lists $300.

    building permit application fee: 25 USD · building permit improvement fee: per 5 USD per 1000 USD improvement cost · zoning change application fee: 200 USD (nonrefundable) · conditional use first application fee: 200 USD · conditional use annual renewal: 150 USD (if permit lapses, entire process begins again) · variance application fee: 125 USD · subdivision platting officer fee: 300 USD

    “$25.00 Application Fee [...] *APPLICATION FEE: $200.00 [...] $125.00 Application Fee [...] Platting Officer fee: $300.00”
    2 more reviewed findings on this topic
    • Published (with conditions) — Mercer County zoning/building-permit application fees.
      “BUILDING PERMITS $25.00 Application Fee $5.00 per $1,000.00 cost of improvements $25.00 per foot for towers / turbines”
    • Published — Mercer County building-permit fees shown on the official zoning page.
      “$25.00 Application Fee * $5.00 per $1,000.00 cost of improvements * $25.00 per foot for towers / turbines”
  • Permit processPublished (with conditions)

    Mercer County building-permit applications and related zoning submissions administered by the Mercer County Zoning office.

    • The page states that property in city limits may require contacting the applicable city or village hall.
    • The application must include lot or tract dimensions, the exact location of proposed buildings and structures, and other information required by the Zoning Officer.
    • The page publishes a $25.00 application fee, $5.00 per $1,000.00 of improvement cost, and $25.00 per foot for towers or turbines.

    application fee: 25 USD · improvement-cost fee: per 5 USD per $1,000.00 of improvement cost · tower/turbine fee: per 25 USD per foot

    “BUILDING PERMITS $25.00 Application Fee * $5.00 per $1,000.00 cost of improvements * $25.00 per foot for towers / turbines”
    2 more reviewed findings on this topic
    • Partial — Mercer County zoning, building-permit, conditional-use, variance, and subdivision application processes.
      “All applications must be submitted to the zoning officer at least THIRTY (30) DAYS prior to The zoning board meeting at which it will be reviewed.”
    • Published (with conditions) — Mercer County zoning applications, zoning changes, conditional uses, variances, and building permits
      “All applications must be submitted to the zoning officer at least THIRTY (30) DAYS prior to The zoning board meeting at which it will be reviewed.”

Illinois rules that apply here

  • Building permitLimited

    Privately funded construction in Illinois; the State does not itself issue building permits, while any required permit is addressed by the applicable local government.

    • Permit requirements may be imposed and administered by the municipality, village, city, or county having jurisdiction.
    • The Illinois Capital Development Board states that statewide building codes became effective 1/1/2025, while local code officials remain the best source for project-specific answers.

    statewide building-code effective date: 2025-01-01

    “No. If any of these are required, they would be addressed by the unit of local government.”
    One more reviewed finding on this topic
    • Not required — Issuance of building permits by the State of Illinois for privately funded construction.
      “No. If any of these are required, they would be addressed by the unit of local government.”
  • Owner-builder exemptionConditional

    Owner occupants or lessee occupants of single-family residences, and owners of single-family residences under construction for their own occupancy, performing plumbing planning, installation, alteration, or repair in Illinois.

    • The exemption is limited to plumbing work on the specified single-family residence; the cited statute does not establish a general owner-builder exemption for all construction trades or a statewide exemption from building permits.
    • The plumbing must comply with the minimum standards in the Illinois State Plumbing Code.
    • The plumbing is subject to inspection by the Illinois Department of Public Health or by the local governmental unit if it retains a licensed plumber as inspector.
    • The owner, owner occupant, or lessee occupant may not employ anyone other than a plumber licensed under the Illinois Plumbing License Law to assist.
    • An occupant must have taken possession of and be living in the premises as their bona fide sole and exclusive residence, or, for a residence under construction, expect to take possession and live there as that residence, with current intent to live there for at least 6 months after completion of the plumbing work or, for a residence under construction, at least 6 months after completion of construction.
    • Failure to possess and live in the premises as a sole and exclusive residence for 6 months or more creates a rebuttable presumption that the required intent was lacking.

    minimum occupancy period: >= 6 months (After completion of plumbing work; for a residence under construction, after completion of construction.)

    “Nothing herein contained shall prohibit the owner occupant or lessee occupant of a single family residence, or the owner of a single family residence under construction for his or her occupancy, from planning, installing, altering or repairing the plumbing system of such residence”
    2 more reviewed findings on this topic
    • Conditional — Privately funded construction in Illinois, including projects performed by an owner-builder, as to state-issued building permits, state plan review, state building-code inspections, and state occupancy permits.
      “No. If any of these are required, they would be addressed by the unit of local government.”
    • Conditional — Statewide treatment of local plumbing permits and inspections for qualifying owner occupants performing plumbing work on a single-family residence.
      “Nothing contained in this Act shall prohibit any city, town, village, township or county from providing for a Plumbing Inspector or from requiring permits for the installation and repair of plumbing and collecting a fee therefor, but a city, town, village, township, or county that requires a permit for installation and repair of plumbing may not issue that permit without verification that the applicant has a valid plumbing license or that the applicant is the owner occupant of a single family residence that is the subject of the permit.”
  • Building code adoptedPartial

    Building-code requirements statewide in Illinois, including residential and commercial construction subject to the Capital Development Board Act baseline requirements.

    • Effective 2025-01-01, Illinois requires statewide baseline building-code requirements.
    • Local governments may adopt building codes, but they are not required to adopt codes; jurisdictions that do not adopt a code are treated as non-building-code jurisdictions and must follow the applicable state-law baseline requirements.
    • For jurisdictions with adopted codes, local codes must regulate structural design at least as stringently as the applicable IRC, IBC, or IEBC baseline.
    • Commercial buildings in non-building-code jurisdictions and state-funded buildings are subject to the state-listed codes and qualified-inspection requirements.
    • Residential requirements differ depending on whether the jurisdiction has adopted a compliant building code and whether the home purchaser and builder agree to an alternative code.

    statewide baseline effective date: 2025-01-01 · local code structural minimum for residential buildings: IRC minimum structural requirements · local code structural minimum for commercial new buildings: IBC minimum structural requirements · local code structural minimum for existing commercial buildings: IEBC minimum structural requirements

    “The State of Illinois recently passed legislation (Public Act 103-0510) changing the Capital Development Board Act to require statewide building codes effective 1/1/2025. [...] Commercial buildings in jurisdictions that have not adopted a building code AND state funded buildings. [...] Starting 1/1/25 local codes must regulate the structural design in a manner that is at least as stringent as the IBC© for new buildings or IEBC© for existing buildings. [...] Residential buildings in jurisdictions that have not adopted a building code where agreed to by the home purchaser and home builder. [...] Residential buildings in jurisdictions that have adopted a building code. [...] Starting 1/1/25 local codes must regulate the structural design in a manner that is at least as stringent as the IRC©.”
    3 more reviewed findings on this topic
    • Partial — Illinois Energy Conservation Code requirements applicable to new buildings and structures in Mercer County when a building-permit application is received by a municipality or county.
      “Except as otherwise provided in this Act, the Code shall apply to (i) any new building or structure in this State for which a building permit application is received by a municipality or county and (ii) beginning on the effective date of this amendatory Act of the 100th General Assembly, each State facility specified in Section 4.01 of the Capital Development Board Act. In the case of any addition, alteration, renovation, or repair to an existing residential or commercial structure, the Code adopted under this Act applies only to the portions of that structure that are being added, altered, renovated, or repaired.”
    • Adopted — Statewide Illinois building-code requirements, including buildings in Mercer County, beginning January 1, 2025.
      “The State of Illinois recently passed legislation (Public Act 103-0510) changing the Capital Development Board Act to require statewide building codes effective 1/1/2025.”
    • Adopted — Statewide baseline building-code requirements for residential construction in Illinois, including jurisdictions with and without locally adopted building codes.
      “Please be advised that the State of Illinois recently passed legislation (Public Act 103-0510) changing the Capital Development Board Act to require statewide baseline building codes effective 1/1/2025. Locally adopted building codes must comply with the requirements of the Act.”
  • InspectionsLimited

    Privately funded construction statewide in Illinois, as to inspections performed by the State rather than by a local authority having jurisdiction.

    • The Illinois Capital Development Board does not perform building-code inspections for privately funded construction.
    • If inspections are required, they are addressed by the applicable unit of local government.
    • A local municipality or county may be a non-building-code jurisdiction, in which case applicable state baseline requirements and inspection-certification provisions may apply.
    “No. If any of these are required, they would be addressed by the unit of local government.”
    One more reviewed finding on this topic
    • Not required — Building-code-compliance inspections performed by the State of Illinois for privately funded construction.
      “No. If any of these are required, they would be addressed by the unit of local government.”
  • Certificate of occupancyLimited

    Occupancy permits or certificates for privately funded construction in Illinois.

    • The State does not issue occupancy permits for privately funded construction.
    • If an occupancy permit is required, it is addressed by the applicable unit of local government.
    “No. If any of these are required, they would be addressed by the unit of local government.”
    One more reviewed finding on this topic
    • Not required — Issuance of occupancy permits or certificates by the State of Illinois for privately funded construction.
      “No. If any of these are required, they would be addressed by the unit of local government.”
  • SetbacksDistrict specific (with conditions)

    County zoning regulations for building or setback lines outside municipalities with municipal zoning ordinances.

    • The actual setback distances are established by applicable county zoning districts or other local ordinances.
    • Agricultural buildings may be required to conform to building or setback lines.
    “to establish building or setback lines”
  • Building heightDistrict specific (with conditions)

    County zoning districts outside municipalities with municipal zoning ordinances.

    • The applicable county zoning ordinance determines the actual height limit by district or use.
    • No single statewide height measurement was identified.
    “including height of buildings and structures”
  • Septic inspectionLimited

    New and replacement surface-discharging private sewage disposal systems covered by Illinois EPA general NPDES Permit ILG62.

    • Coverage under the general permit is limited to eligible dischargers.
    • Systems not eligible for general-permit coverage may require an individual NPDES permit.
    • Periodic inspection, monitoring, and reporting are required under the permit.
    “The permit sets discharge limits and requires periodic inspection, monitoring and reporting.”
  • Off-grid sanitationAllowed (with conditions)

    Off-grid disposal of human wastes through privies, portable toilets, recirculation toilets, incinerator toilets, and compost toilets statewide in Illinois.

    • Other domestic wastes must be disposed of in a conventional private sewage disposal system.
    • Compost toilets may also be used for other organic domestic wastes.
    • Privies have construction, capacity, venting, maintenance, and abandonment requirements.
    • A privy pit must have a minimum capacity of 50 cubic feet per seat.
    • A privy must be pumped when filled to within 18 inches of the bottom of the riser.
    • Vault privies are required where groundwater or limestone formations are within 4 feet of the bottom of the pit.
    • Recirculating toilets must meet NSF International/ANSI Standard 41 and residuals must go to an approved public or private sewage disposal system.
    • Incinerator and compost toilets have separate maintenance and disposal requirements; compost toilets must meet NSF International/ANSI Standard 41.

    privy pit minimum capacity: >= 50 cubic feet per seat · privy pumping trigger: <= 18 inches from bottom of riser (Pump when filled to within this distance.) · vault-privy groundwater or limestone separation: < 4 feet from bottom of pit (Watertight, non-metal vaults are required where the condition applies.)

    “Privies, portable toilets, recirculation toilets, incinerator toilets and compost toilets are approved for private sewage disposal of human wastes.”
  • Well permitRequired

    Construction of a new water well, modification of an existing water well, or sealing of an abandoned water well in Illinois.

    • A permit must be obtained from the Illinois Department of Public Health or an approved local health department before work begins.
    • The application must use Department or approved local health department forms and include a plan and drawing of the proposed construction.
    • The plan must include the lot size, slope, property lines, distances to septic tanks, abandoned wells, property lines, seepage fields, sewers, and other contamination sources; driller license number and name; estimated daily pumping capacity if greater than 100,000 gallons per day; well location; owner name and address; well type; estimated depth; well-use type; and proposed aquifer.
    • The permit is void if construction has not commenced within one year after issuance.
    • The permit fee for constructing, deepening, modifying, or sealing a water well may not exceed $100.
    • The Department will deny a permit request when available information indicates groundwater contamination exceeds Class I groundwater standards, subject to the treatment approval provision in subsection (f)(2).
    • The permittee must notify the Department, approved local health department, or approved unit of local government by telephone or in writing at least two days before work begins.

    maximum water well permit fee: <= 100 USD · permit commencement deadline: 1 year after issuance (Permit is void if construction has not commenced within that period.) · pre-work notification: >= 2 days (Notification may be by telephone or in writing.)

    “A permit to construct a new water well, modify an existing water well or seal an abandoned water well shall be obtained from the Department or approved local health department prior to start of work.”
  • Driveway accessRequired

    Work within the right-of-way of an Interstate, U.S. state route, Illinois state route, or state-maintained roadway, including access-driveway requests to State highways.

    • A permit must be obtained before work begins.
    • Requirements may vary by IDOT district; the applicant must contact the district office for specific requirements.
    • IDOT's access-driveway handbook guides what is allowable for highway access requests.
    “Per 605 ILCS 5/4 209, IDOT requires a permit when working within the right-of-way of an Interstate, U.S. state route, Illinois state route, or state maintained roadway. A permit must be obtained prior to the start of any work and a copy of the approved permit must be at the worksite at all times.”
  • Building in a floodplainRequired

    Construction activities in regulated Illinois floodways and, where a floodway has not been delineated, generally work anywhere in the floodplain.

    • For downstate streams, IDNR Division permitting applies to floodways of streams draining at least one square mile in urban areas or ten square miles in rural areas.
    • In northeastern Illinois, Part 3708 applies to identified floodways in Cook County excluding Chicago, DuPage, Kane, Lake, McHenry, and Will Counties.
    • Some minor activities are automatically authorized by statewide or regional permits if their terms and conditions are met.
    • For State-owned property, Part 3710 requires a permit for all development activity in FEMA-mapped floodplains.

    urban stream drainage area threshold: >= 1 square mile (regulated floodways under Part 3700) · rural stream drainage area threshold: >= 10 square miles (regulated floodways under Part 3700)

    “All construction activities in the floodways of streams (the channel and the adjacent portion of the floodplain that is needed to safely convey and store flood waters) in urban areas where the stream drainage area is one square mile or more or in rural areas where the stream drainage area is ten square miles or more must be permitted by the Division prior to construction.”
  • Short-term rentalsLimited

    Short-term rentals in Illinois where at least one room is rented for fewer than 30 consecutive days and accommodations are reserved in advance, when the hosting platform meets the statutory definition of a re-renter.

    • Beginning July 1, 2025, qualifying hosting platforms are subject to Hotel Operators’ Occupation Tax.
    • The source establishes tax and registration obligations, not statewide land-use permission; local zoning and licensing may separately apply.

    rental period: < 30 consecutive days

    “Beginning July 1, 2025, hosting platforms for short-term rentals that meet the definition of “re-renter” are subject to Hotel Operators’ Occupation Tax.”
  • Campground & park staysAllowed (with conditions)

    Overnight camping in Illinois campgrounds subject to the Campground Licensing and Recreational Area Act.

    • IDPH annually inspects and licenses campgrounds in Illinois.
    • The state campground definition includes camping and temporary parking of recreational vehicles.
    • Campgrounds within home rule units of government are exempt from the state campground licensing requirement.
    • Recreational areas without overnight camping, such as highway rest stops and picnicking areas, are subject to the rules but are not licensed or routinely inspected.

    minimum persons for statutory campground threshold: >= 10 persons · minimum camping duration for statutory campground threshold: >= 6 camping days per calendar year

    ““Camping Day” means any 24 hour period or portion thereof during which the participants remain overnight at the site.”
  • county building authorityLimited

    County building-construction and building-code regulation, including residential structures, in counties meeting the statutory population and metropolitan-area conditions.

    • The county must have a population not in excess of 1,000,000.
    • The county must be located in the area served by the Northeastern Illinois Metropolitan Area Planning Commission.
    • Rules are subject to rules or regulations adopted by the State Fire Marshal under the cited gasoline and volatile-oils statute.
    • The county must exempt municipalities located wholly or partly within the county when the municipal building code is equal to the county regulation and local authorities are enforcing that municipal code.
    • The rules apply throughout the county, but municipalities may establish higher standards.
    • The rules do not apply to construction or alteration of buildings or structures used or to be used for agricultural purposes on a tract zoned and used for agricultural purposes.
    • The county board must follow the publication and posting requirements in 55 ILCS 5/5-1063.
    • Beginning on the effective date of the amendatory Act of the 92nd General Assembly, a county adopting a new building code or amending an existing building code must provide the building-code identification to the Capital Development Board under Section 10.18 at least 30 days before adoption.
    • Violations are petty offenses, and enforcement is by an officer designated by county-board resolution.
    • The provision expressly authorizes county building-construction and building-code rules, but the opened text does not expressly use the phrase residential building permit requirement.

    population threshold: <= 1000000 persons (The county must be located in the area served by the Northeastern Illinois Metropolitan Area Planning Commission.) · pre-adoption identification period: >= 30 days (Applies to a new building code or amendment under the stated amendatory-Act provision.)

    “The county board in any county with a population not in excess of 1,000,000 located in the area served by the Northeastern Illinois Metropolitan Area Planning Commission may prescribe by resolution or ordinance reasonable rules and regulations (a) governing the construction and alteration of all buildings and structures and parts and appurtenances thereof and governing the maintenance thereof in a condition reasonably safe from the hazards of fire, explosion, collapse, contagion and the spread of infectious disease”
    One more reviewed finding on this topic
    • General — Illinois counties adopting and enforcing building codes and issuing building permits for residential construction in unincorporated areas, subject to the statewide baseline framework.
      “A municipality or county is not required to adopt building codes. If they do NOT adopt a building code then they are considered a non-building code jurisdiction and section 10.09-1 of the Capital Development Board Act (20 ILCS 3105) applies. If they do adopt a building code(s) then it must comply with section 10.18 of the Capital Development Board Act (20 ILCS 3105).”

Still unanswered

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

  • Zoning districts — Published county zoning districts in Mercer County.
  • Minimum dwelling size — Minimum dwelling-size requirements in Mercer County.
  • Minimum lot size — Minimum lot-size requirements in Mercer County.
  • Lot coverage — Lot-coverage requirements in Mercer County.
  • Camping on your land — Temporary camping on private land in Mercer County.
2 more unanswered
  • Tiny homes
  • Accessory dwellings

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, Illinois

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

Mercer County scores 65/100 on the Bolthole Index, a strong county profile. Its strengths: mixed durability signals and sparse surroundings — about 6,684 people within a 30-minute drive.

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

Mercer County generally requires a residential building permit, and it enforces county zoning. Onsite septic is permitted by Mercer County Health Department (under Illinois Department of Public Health Private Sewage Disposal Code). 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, Illinois?

Land in Mercer County runs about $9,250 per acre, based on the latest county data.

What is the water situation in Mercer County?

Mercer County gets about 37.8" of rain a year, with severe drought in roughly 4.1% of years.

How remote is Mercer County?

A representative private-land location has about 6,684 people within a 30-minute drive and 1,447,405 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 Illinois

Compare side-by-side →See all 102 Illinois counties ranked →