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 is the listed onsite-wastewater permitting authority for 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 is the listed Mercer County onsite-wastewater authority56
Septic permit
Required for most installations and repairs; some single-family lots may be exempt7
RV or tiny-home living
No Mercer County occupancy rule was confirmed; ask the County Commission or County Clerk234
Owner-builder exemption
No county-specific exemption was confirmed8
Septic soil difficulty
County soils are rated severely limited for conventional drain fields9

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

[email protected]

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 September 28, 2026.

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, subdivision issue, or county-road requirement affects the site34. Septic has a named authority: the Missouri Department of Health and Senior Services lists its Onsite Wastewater Treatment Program for Mercer County56. DHSS directs Mercer County applicants to submit project information through its online form to request an application number6. 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-way13.

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 it14. 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 lists itself as Mercer County's onsite-wastewater permitting authority and tells applicants to use the state's request form to obtain an application number56. A construction permit is required before installing or repairing most onsite systems, while some single-family residential lots may qualify for an exemption7. Residential property under 3 acres requires a permit, subject to county-specific exceptions, and work should wait until DHSS issues the permit or confirms an exemption7. DHSS or a local agency covers qualifying domestic systems at or below 3,000 gallons per day, while Missouri DNR handles larger flows and other specified systems15. Soil evaluation deserves early attention because 0% of Mercer County soils are rated without severe limits for a conventional drain field9. For an existing home, a private licensed inspector can assess the system because local public-health agencies generally no longer perform transfer inspections16.

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 ground17.

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, subdivision, 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 field9.
  1. Request an application number from Missouri DHSS and obtain the required construction permit, or confirmation of an exemption, before installing or repairing the onsite system76.
  1. If the driveway enters a state highway, obtain MoDOT's right-of-way permit before construction13.
  1. Ask the appropriate Missouri water authority about private-well requirements because no Mercer County-specific well-permit answer could be confirmed.

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 less918. 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 jurisdiction193. Confirm legal road access, and obtain a state permit if a new or modified driveway enters MoDOT right-of-way13. 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 center2021. The effective property-tax rate is about 0.9%, with a median annual property-tax bill of $9052223.

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 budget9.
  • Missouri's onsite-sewage application-fee suspension took effect in 2026 and is temporary, so confirm the current charge with DHSS when requesting an application number76.

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. Missouri DHSS — OWTS Construction Permit Required (2026 county census)
  6. Missouri DHSS Onsite Wastewater Treatment Program (health.mo.gov)
  7. OWTS Construction Permit Process (Missouri statewide rule), quoted and re-checked
  8. (2026 county census)
  9. Share of soils without severe limits for a conventional septic drain field (USDA SSURGO): Bolthole Index county data
  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. Permits | Missouri Department of Transportation (Missouri statewide rule), quoted and re-checked
  14. RSMo § 64.090 — Planning and zoning powers of county commission (Missouri statewide rule), quoted and re-checked
  15. On-site Septic Systems and Subdivisions (Missouri statewide rule), quoted and re-checked
  16. Onsite Wastewater Treatment System Inspections Versus Evaluations (Missouri statewide rule), quoted and re-checked
  17. Frequently Asked Questions (Missouri statewide rule), quoted and re-checked
  18. Share of land at 15% slope or less: Bolthole Index county data
  19. Laws and Regulations That Might Affect You if You Mine Sand or Gravel From Missouri Streams (Missouri statewide rule), quoted and re-checked
  20. Population density: Bolthole Index county data
  21. Distance to the nearest metro area: Bolthole Index county data
  22. Effective property tax rate: Bolthole Index county data
  23. Median property tax bill: Bolthole Index county data

Written September 28, 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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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%Septic soil without severe limits
0 acWorkable land screen
29.9%Wooded land
44 tonsBiomass / forest ac
51.5°FAvg temp

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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

  • 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”
  • Who permits septicMixed

    Missouri wastewater treatment systems, including domestic onsite systems, larger-flow systems, direct discharges, lagoons, subdivisions, and industrial wastewater.

    • DNR regulates direct point-discharge or surface-land-application systems, non-individual lagoons, facilities exceeding 3,000 gallons per day, and industrial process waste.
    • DHSS or a local agency, typically the county health department, regulates single-family subsurface onsite systems, individual single-family lagoons, and qualifying systems at or below 3,000 gallons per day.
    • Local agencies may administer qualifying systems under local authority or ordinance.

    domestic wastewater flow threshold: <= 3000 gallons per day (DNR regulates facilities with domestic wastewater flow greater than 3,000 gallons per day)

    “In Missouri, different state and local agencies are responsible for regulating wastewater treatment systems.”
  • Septic permitRequired

    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 OWTS.
    • Some single-family residential lots may be exempt.
    • For residential property less than three acres, a permit is required; the exemption does not apply in some counties, so the county authority must be checked.
    • Work should not begin until a permit is issued or an exemption is confirmed.
    • Effective August 28, 2026, application fees for onsite sewage disposal system construction, modifications, and repairs are temporarily suspended.

    residential lot threshold: < 3 acres (The exemption does not apply in some counties.) · temporary permit-fee suspension effective date: 2026-08-28 (Applies to application fees associated with onsite sewage disposal system construction, modifications, and repairs.)

    “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.”
  • 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.”
  • 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.”
  • Agricultural exemptionAvailable (with conditions)

    Erection, maintenance, repair, alteration, or extension of farm buildings or farm structures as against county fire-protection or fire-prevention ordinances.

    • The exemption applies to fire protection or fire prevention ordinances adopted by counties in Missouri.
    • The statutory text addresses farm buildings and farm structures; it does not establish a general exemption from every zoning, building-code, floodplain, septic, or other land-use requirement.
    • Effective August 28, 2025.

    effective date: 2025-08-28

    “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.”
  • 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.”
  • 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.”
  • Permit processPublished (with conditions)

    Permit applications for work on Missouri Department of Transportation right-of-way statewide.

    • The process applies to MoDOT right-of-way work.
    • Applicants may apply online, contact the area Traffic Specialist, or submit a hard-copy application by mail.
    • Additional documentation may be required depending on the work, including site plans, performance bond, certificate of liability, traffic studies, or a meeting with MoDOT personnel.
    • After issuance, Missouri One Call, a Notice of Intent, permit and approved-plan retention, and Traffic Specialist contact requirements apply.
    • Lane closures require a request at least two working days in advance and authorization before closing lanes.
    • The Traffic Specialist must be contacted at least 48 hours before beginning work and for necessary inspections.

    lane-closure advance request: >= 2 working days (authorization from MoDOT is also required) · Traffic Specialist pre-work contact: >= 48 hours (before beginning work)

    “Contact the Traffic Specialist a minimum of 48 hours prior to beginning work and for all necessary inspections.”
  • county zoning authorityGeneral

    Missouri counties adopting zoning regulations for unincorporated territory.

    • First-class charter counties are empowered under RSMo § 64.090; that section excludes first-class counties without a charter form of government.
    • A first-class noncharter county or a county of the second, third, or fourth class may establish county zoning under RSMo §§ 64.845 to 64.880 only after the zoning question is submitted to county voters and a majority of votes cast favors county zoning.
    • The authority applies to unincorporated portions or territory and does not apply to incorporated portions under § 64.090.
    • Section 64.090 excludes specified agricultural activities and certain farm structures, underground mining, and protects existing lawful uses subject to gradual elimination of nonconforming uses.
    “If a majority of the votes cast is in favor of county zoning, the county commission shall proceed with a program of county zoning”
  • county building authorityLimited

    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.

    • RSMo § 64.170 grants the authority to counties of the first and second classification only.
    • The authority is subject to subsections 2 and 3.
    • A county that had not adopted a building code before August 28, 2001, under §§ 64.170 to 64.200, lacks authority to adopt one under those sections unless voters approve it.
    • The building-code authority vote is limited to voters in the affected area; a code affecting a county may not be voted on by citizens of incorporated territory.
    • The statute authorizes building regulations, building permits, inspections, licensing rules, and permit, license, and inspection fees.
    “the county commission in all counties of the first and second classification [...] is for this purpose empowered [...] to adopt [...] regulations to control the construction”

Still unanswered

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

  • Owner-builder exemption — Owner-builder construction in unincorporated Mercer County.
  • Inspections — Building inspections in unincorporated Mercer County.
  • Certificate of occupancy — Certificates of occupancy for buildings in unincorporated Mercer County.
  • County-wide zoning — Countywide zoning authority in Mercer County, Missouri.
  • Local zoning — Local zoning within Mercer County, including incorporated municipalities and unincorporated areas.
15 more unanswered
  • Zoning districts
  • Minimum dwelling size
  • Minimum lot size
  • Setbacks
  • Lot coverage
  • Building height
  • Living in an RV
  • Camping on your land
  • Tiny homes
  • Manufactured homes
  • Accessory dwellings
  • Well permit
  • Mandatory utility hookup
  • Subdividing land
  • 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. 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.

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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How Mercer compares in Missouri

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