Bolthole Index

Washington County, Missouri

Building permits, zoning and septic rules in Washington County, Missouri

72Index Score / 100
#49 of 115 in Missouri

Unincorporated Washington County, Missouri does not require a general building permit, while Potosi requires building permits for specified construction and structural changes12. Potosi also has municipal zoning, but countywide zoning for unincorporated land could not be confirmed3. Septic permits remain separate: the Washington County Health Department administers qualifying systems countywide, subject to city and state jurisdictional exceptions4.

At a glance

Building permit
No general building permit in unincorporated areas; Potosi requires building permits for specified work12
Zoning
Potosi has municipal zoning; countywide zoning for unincorporated land could not be confirmed3
Septic permits
Washington County Health Department handles qualifying OWTS permits under its own ordinance4
Owner-builder
We could not confirm a general owner-builder exemption; ask the County Commission and the municipality, if any56
Farm structures
County fire ordinances cannot require building permits for farm structures; other requirements can still apply7
Private wells
Well and pump installers need the applicable state permit; a landowner may do their own work without one8
Floodplain development
Some type of permit must be issued for all development in a mapped floodplain, through whichever community participates9
Septic exemptions
Most installations and repairs need a permit; confirm any residential-lot exemption before work104

Who to call

Also useful

Washington County Commission

County governing body; commissioners meet at the courthouse in Potosi and are the first call for land-use questions since there is no county building or zoning department

573-436-7704

102 North Missouri Street, Potosi, MO 63664

Also useful

Washington County Clerk's Office

County recording, elections and licensing; supports the county commission's operations

573-436-7704

jallen@washcomo.us

102 North Missouri Street, Potosi, MO 63664

Septic permits

Washington County Health Department, Environmental Health (OWTS)

OWTS (septic) construction permits, the county's soil evaluators list, and registered installer applications for Washington County

573.438.2164

info@wcmohealth.org

520 Purcell Drive, Potosi, MO 63664

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 Washington 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 Washington County, Missouri?

A general building permit is not required for a home in unincorporated Washington County, Missouri1. Confirm the parcel is outside an incorporated city before relying on that answer: Potosi requires a written building-permit application before starting a new building, structure, parking lot, or sign, or enlarging or structurally altering one2. Potosi's code official may inspect permitted premises before a certificate of occupancy is issued; inspection of other premises requires reasonable cause to believe a violation exists11. Potosi also requires a certificate of occupancy before a newly erected or structurally altered building is occupied or used12. A county fire-protection ordinance cannot require a building permit for farm structures, but that narrow protection does not remove septic permits, floodplain permits, or municipal requirements7. We could not confirm a general owner-builder exemption; ask the County Commission and the municipality governing the parcel56.

Who issues building permits in Washington County?

Washington County has no general building-permit process for an unincorporated home, so call the Washington County Commission when the parcel's county contact is unclear16. Inside Potosi, the city issues building permits for specified construction and structural changes and administers the related certificate of occupancy212. Potosi's building-permit and zoning authority does not replace septic review: the Washington County Health Department administers qualifying onsite wastewater systems, with incorporated-area and state-agency exceptions413. The Clerk's Office maintains official documents, issues licenses, and supports County Commission operations, so it can help locate county records or the correct county contact14. An entrance onto a state highway may need Missouri Department of Transportation approval15. Development in a mapped floodplain needs the applicable community's floodplain permit, and work in a regulatory floodway needs an engineering No-Rise Certificate before that permit can issue9.

Does Washington County have zoning?

Potosi has zoning for buildings, structures, and land uses inside its corporate limits3. We could not confirm countywide zoning for unincorporated Washington County or zoning status in every other municipality, so ask the Washington County Commission and the relevant city before assuming a parcel has no zoning approval requirement36. We also could not confirm county rules for minimum dwelling size, minimum lot size, setbacks, lot coverage, building height, or subdivision; ask about the specific parcel rather than treating silence as permission6. Missouri law authorizes counties to adopt zoning, but that authority does not establish Washington County's current rules16. Potosi zoning stays municipal, while septic permits for qualifying systems remain with the Washington County Health Department subject to incorporated-area and state-agency exceptions34.

How do septic permits work in Washington County?

The Washington County Health Department administers qualifying onsite wastewater treatment systems under a county ordinance that may be stricter than Missouri's minimum standards413. Missouri's baseline requires a septic construction permit for a residential property under 3 acres and for every nonresidential system regardless of tract size, but the residential acreage exemption does not apply in every county10. Ask the Health Department to confirm whether Washington County recognizes an exemption before installation or repair begins413. Missouri DNR handles specified systems outside ordinary local coverage, including surface discharges, non-single-family lagoons, industrial wastewater, and systems over 3,000 gallons per day4. Only about 2% of Washington County soils lack severe limitations for a conventional drain field, so make septic feasibility an early purchase condition17. Missouri does not impose a universal sale inspection for every existing system; a buyer, lender, or local rule may still require an evaluation18.

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

We could not confirm a Washington County rule that either allows or prohibits full-time RV living, temporary camping, a tiny house on wheels, or a tiny home on a foundation. Ask the Washington County Commission about an unincorporated parcel and the governing city about land inside city limits; Potosi applies municipal zoning within its corporate limits63. Building-permit and zoning answers do not settle sanitation: Missouri allows onsite wastewater treatment where public sewer is unavailable, subject to the Washington County ordinance and applicable approvals19. The Washington County Health Department remains the septic-permit contact for qualifying systems even where a city handles building permits or zoning, subject to incorporated-area and state-agency exceptions413. Before buying for RV or tiny-home use, get separate answers on zoning approval, building permits, septic permits, floodplain permits, and road access from the authority responsible for each.

What are the steps to build a home in Washington County?

  1. Confirm whether the parcel is unincorporated or inside a city; Potosi requires building permits for specified construction and structural changes2.
  1. Ask the County Commission and any governing city whether zoning approval, setbacks, county-road access review, or a floodplain contact applies63.
  1. Arrange the septic site evaluation early because only about 2% of county soils lack severe limitations for a conventional drain field17.
  1. Obtain the septic permit from the Washington County Health Department, or confirmation of an exemption or different agency, before installation or repair41013.
  1. For a private well, use an installer with the applicable state well or pump permit; a landowner may install their own well or pump without that permit8.
  1. Secure any state-highway entrance approval and applicable floodplain permit before site work159.
  1. Obtain Potosi's certificate of occupancy when required; an unincorporated home has no general county building permit121.

What should you check before buying land in Washington County?

Only about 2% of Washington County soils lack severe limitations for a conventional drain field, so make an acceptable site evaluation and septic design a purchase condition17. About 50.7% of the county is at a slope of 15% or less, while 86.2% is wooded; inspect the actual homesite and access route before budgeting for clearing, grading, and drainage2021. Federal land covers about 17.1% of the county, so verify boundaries, legal access, and any neighboring public ownership on the parcel map22. Check the current flood map because development in a mapped floodplain needs a permit through the applicable community9. Washington County's effective property-tax rate is about 0.6%, its median annual property-tax bill is about $682, its typical home value is about $196,763, and farmland averages about $2,926 per acre; parcel-specific assessments can differ23242526.

Watch-outs

  • Call the Washington County Commission to identify who handles access from a county road and which community administers floodplain permitting for a specific parcel69.
  • We could not confirm minimum lot size, setbacks, building height, subdivision, or RV and tiny-home occupancy rules for unincorporated land; ask the County Commission before relying on an assumed absence of regulation6.
  • Potosi has its own zoning, building-permit, inspection, and certificate-of-occupancy rules, while qualifying septic systems remain under the Washington County Health Department subject to jurisdictional exceptions3211124.

Sources

  1. State of Missouri - County Building Codes dataset (2026 county census)
  2. Chapter Twenty-six: Planning and Zoning, quoted and re-checked
  3. Government — City of Potosi, Missouri, quoted and re-checked
  4. OWTS Construction Permit Process, quoted and re-checked
  5. (2026 county census)
  6. Washington County Commission (washingtoncountymo.us)
  7. RSMo Section 64.003, quoted and re-checked
  8. Water Wells - PUB2945, quoted and re-checked
  9. Floodplain Forms, quoted and re-checked
  10. health.mo.gov, quoted and re-checked
  11. Potosi Code, Chapter 5, Buildings, quoted and re-checked
  12. Potosi Code, Chapter 26, Planning and Zoning, quoted and re-checked
  13. Washington County Health Department, Environmental Health (OWTS) (wcmohealth.org)
  14. Washington County Clerk's Office (washingtoncountymo.us)
  15. Types of Entrances Requiring Permits, quoted and re-checked
  16. RSMo § 64.090 — Planning and zoning powers of county commission (Missouri statewide rule), 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, quoted and re-checked
  19. Onsite Wastewater Treatment, quoted and re-checked
  20. Share of land at 15% slope or less: Bolthole Index county data
  21. Wooded share of land: Bolthole Index county data
  22. Federal land share: Bolthole Index county data
  23. Effective property tax rate: Bolthole Index county data
  24. Median property tax bill: Bolthole Index county data
  25. Typical home value (Zillow): Bolthole Index county data
  26. Farmland value per acre (USDA census): 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

RuleWashington CountySt. Francois CountyCrawford CountyJefferson CountyIron CountySte. Genevieve CountyDent County
Building permitNot requiredRequiredNot requiredRequiredNot requiredRequiredNot required
County zoningNoNot publishedNoYesNot publishedNot publishedNo
Septic permitsCounty Health Dept.County Health CenterCounty Health Dept.County Code Enforcement Div.DHSSCounty Health Dept.DHSS

County locator

Washington County in Missouri

72
County map
Washington County highlighted among the Missouri counties · colored by Index score

How Washington County scores

Seclusion69100% ev.
Self-Sufficiency53100% ev.
Admin Boringness8790% ev.
Durability48100% ev.
Property Autonomy47100% ev.
Carry Cost83100% 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 →

$197kTypical home
0.6%Property tax
$2,926Land / acre
45.6"Annual rain
5.5% of yrsSevere drought
12.7 / yr (+11)Mid-century 100°F days
15.2 daysMid-century dry spell
1.98" (+8%)Mid-century 1-day rain
1.83×Wildfire change factor
100%Forward climate coverage
$2,122Home insurance / yr
2.5% / yrInsurance growth
1.55%Nonrenewal rate
county median (2+ published ZIPs)Insurance basis
10,317People within 30 min
1,995,254People within 2 hr
36,196Radius comparison (15 mi)
31People / sq mi
17.1%Federal land
50.7%Land at 15% slope or less
2%Soils rated "not limited" for septic (strict USDA rating)
9,566 acWorkable land screen
86.2%Wooded land
43.6 tonsBiomass / forest ac
55°FAvg temp

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Cities and towns in Washington 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.

Village of Caledonia · Irondale · Town of Mineral Point · Potosi

Answers from the rulebook for Washington County

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

Washington County rules

  • Local zoningVaries (with conditions)

    Aggregate local zoning within Washington County; at least the incorporated City of Potosi has municipal zoning, while countywide and other municipal coverage was not established in this search.

    • The Potosi zoning rules apply within the corporate limits of the City of Potosi, not generally to unincorporated Washington County.
    • Other municipalities and any county zoning applicable to unincorporated areas require separate verification.
    “The regulations and restrictions in this Article shall apply to all buildings, structures, and land uses within the corporate limits of the City of Potosi, unless otherwise exempted or grand-fathered by other provisions of this Article.”
  • Who permits septicCounty

    On-site wastewater permitting in Washington County, Missouri, subject to incorporated-area jurisdictional exceptions and the types of systems regulated by state agencies.

    • The Washington County Health Department is identified by Missouri DHSS as the county authority with an ordinance.
    • The county ordinance may impose requirements beyond Missouri minimum construction standards.
    • Missouri DHSS states that some incorporated cities may not fall under a local permitting authority even when a county ordinance is in place; incorporated-area work may be referred back to DHSS.
    • Missouri DNR regulates systems outside DHSS jurisdiction, including systems with flows greater than 3,000 gallons per day, systems discharging to surface waters, non-single-family lagoons, and industrial wastewater systems.

    maximum domestic wastewater flow under DHSS coverage: <= 3000 gallons per day (DNR regulates specified systems outside DHSS coverage)

    “Agency: Washington County Health Dept. Authority Type: Ordinance. Address: 520 Purcell Drive Potosi, MO 63664 County: Washington Phone: (573) 438-2164 Website: www.wcmohealth.org Alert: Contact the agency above for onsite wastewater permitting instructions. This county has their own Onsite Wastewater Ordinance and may have additional requirements beyond the state minimum construction standards.”
  • Septic permitRequired

    Installing or repairing most onsite wastewater treatment systems in Washington County, Missouri, under the Washington County Health Department's onsite wastewater ordinance.

    • The Washington County Health Department is identified by Missouri DHSS as the local permitting agency and Washington County is identified as an ordinance county.
    • Some single-family residential lots may be exempt from permitting; the exemption must be confirmed by the appropriate permitting authority.
    • Washington County may impose requirements beyond Missouri's state minimum construction standards.
    • Work should not begin until a permit has been issued or an exemption to permitting has been confirmed.
    • Some incorporated areas may not fall under the local permitting authority and may be referred back to DHSS.
    • Lagoons serving anything other than a single-family residence, systems discharging to surface waters, systems treating flows greater than 3,000 gallons per day, and industrial wastewater systems are regulated by the Missouri Department of Natural Resources rather than under the ordinary DHSS OWTS coverage.
    “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. [...] Agency: Washington County Health Dept. Authority Type: Ordinance [...] Contact the agency above for onsite wastewater permitting instructions. This county has their own Onsite Wastewater Ordinance and may have additional requirements beyond the state minimum construction standards.”
  • Driveway accessLimited

    Entrance types administered by the Missouri Department of Transportation, including residential driveways, side roads, commercial drives, truck entrances, and paved approaches.

    • The official page identifies permit-required entrance categories but does not state that every road or driveway in Washington County is under MoDOT jurisdiction.
    • Restricted-access entrance configurations may include right-in/right-out, right-in-only, right-out-only, and other listed configurations.
    “Types of Entrances Requiring Permits Typical entrance details Type I: Residential Driveway Type II: Side Road Type III: Commercial Drive Type IV: Truck Pair Type V: Truck Single/Volume Product Paved Appoach”
  • County-wide zoningAbsent

    Washington County does not require permitting for sites outside the city limits of Potosi and has no countywide zoning; land-use controls apply only within incorporated municipalities.

    Meramec Regional Planning Commission - Washington County ↗Scouted from the county site, not yet independently re-checked

Missouri rules that apply here

  • Building permitLimited

    Erection, maintenance, repair, alteration, or extension of farm buildings or farm structures in Washington County, to the extent a county fire-protection or fire-prevention ordinance would otherwise require a permit.

    • RSMo Section 64.003 applies to fire-protection or fire-prevention ordinances adopted by a county; it does not establish that all building permits or permits imposed by other authorities are unnecessary.
    • The statute is effective August 28, 2025.
    “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.”
  • 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”
  • 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.”
    2 more reviewed findings on this topic
    • Limited — Inspection or evaluation of existing onsite wastewater systems, especially in connection with a real-estate transaction, in Washington County.
      “State regulations do not require systems to be brought up to current standards as a result of an inspection/evaluation to be sold.”
    • 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.”
    3 more reviewed findings on this topic
    • Limited — Off-grid domestic sanitation and onsite wastewater disposal in Washington County.
      “No. Your system cannot pose a threat to public health or to the environment.”
    • Allowed (with conditions) — Use of an onsite wastewater treatment system where central sewer service is unavailable in Washington County, subject to the county ordinance and applicable state or local approvals.
      “An estimated 25% of homes in Missouri rely on an onsite wastewater treatment system (OWTS) in areas where public sewers are not available. Onsite systems treat wastewater and disperse it on the property where it is generated. [...] When authority is based on a local ordinance, regulation can be more restrictive than the state standard; check with your local authority.”
    • 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”
    4 more reviewed findings on this topic
    • Limited — Construction, repair, pump installation, or contracted installation of private domestic water wells in Washington County.
      “Landowners may install their own well or pump without a permit pursuant to the above mentioned law and rules.”
    • Limited — Water-well construction or repair in Washington County, including private domestic wells.
      “A non-restricted water well installation permit is required to construct or repair a water well in Missouri. A non-restricted pump installation permit is required to install or replace a pump in a water well. A non-restricted pump installation permit is also needed to install or repair the plumbing and electrical lines from the well to the point of entry in the structure. A restricted water well or pump installation permit is required for someone to contract these activities or to direct the installation. Landowners may install their own well or pump without a permit pursuant to the above mentioned law and rules.”
    • 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)

    Agricultural activities and certain farm structures subject to the county building and land-use restriction powers addressed by Missouri Revised Statutes § 64.890, including Washington County to the extent those statutory powers apply.

    • The exemption does not apply to incorporated portions of counties.
    • The statute excludes the raising of crops, livestock, orchards, or forestry from the referenced county restriction powers.
    • Seasonal or temporary impoundments used for rice farming or flood irrigation are excluded; the statute defines these as small berms of no more than eighteen inches high placed around a field to hold water for growing rice or flood irrigation.
    • The statute does not apply to erection, maintenance, repair, alteration, or extension of farm buildings or farm structures used for those purposes in an area not within the area shown on the flood hazard area map.
    • The statute preserves existing lawful property use and maintenance, judicial review of reasonableness, and authorized public utility services under the listed exceptions.

    rice-farming or flood-irrigation berm height: <= 18 inches (The statute defines qualifying small berms as no more than eighteen inches high.)

    “The provisions of this section shall not apply to the incorporated portions of the counties, nor to the raising of crops, livestock, orchards or forestry”
    5 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.”
    • Available (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.
      “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.”
  • 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 [...]”
    One more reviewed finding on this topic
    • 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.”
  • 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.”
    2 more reviewed findings on this topic
    • Required — All development in the floodplain in Washington County, subject to the applicable community floodplain-management process.
      “This sample Floodplain Development Permit was developed by the State and can be used “as is” or modified to fit the community’s permit process. Regardless, some type of permit MUST be issued for ALL development in the floodplain. An Engineering “No-Rise” Certificate is required for all proposed development in the regulatory floodway, and must be obtained by the community before the floodplain development permit may be issued.”
    • 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.”
    One more reviewed finding on this topic
    • 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.”
    One more reviewed finding on this topic
    • 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”

Inside cities and towns in Washington County

Municipal rules found while researching the county. They apply inside that city or town, not to unincorporated land.

  • Building permitRequired

    New buildings, structures, parking lots, signs, and enlargement or structural alteration within the City of Potosi.

    • A written application must be filed and a building permit obtained before starting construction or the stated enlargement or alteration.
    • Applications must comply with the Potosi zoning article and building code.
    • A plat in duplicate, drawn to scale, must be filed in the form prescribed by the Building Commissioner and include required location and other information.
    • Failure to provide required information may justify permit revocation.
    • The Board of Adjustment may issue a written order allowing a permit or certificate of occupancy where the construction, addition, or alteration would otherwise violate the article.
    “It shall be unlawful to start the construction of a new building, structure, parking lot, or sign or the enlargement or structural alteration of a building, structure, parking lot, or sign, without first filing a written application for and obtaining a building permit.”
    One more reviewed finding on this topic
    • Required — New buildings, structures, parking lots, signs, and enlargements or structural alterations within the City of Potosi.
      “It shall be unlawful to start the construction of a new building, structure, parking lot, or sign or the enlargement or structural alteration”
  • InspectionsLimited

    Inspection authority for dwellings, dwelling units, and premises within the City of Potosi, Washington County, Missouri.

    • For a structure or premises for which a permit has been issued but no certificate of occupancy has been received, the code official may enter at any reasonable time.
    • For other structures or premises, inspection authority requires reasonable cause to believe that a code violation exists.
    • Inspections are subject to constitutional restrictions on unreasonable searches and seizures.
    • If entry is refused or not obtained, the code official may pursue recourse as provided by law.
    “The code official shall have the authority to enter at any reasonable time any structure or premises for which a permit has been issued but has not received a certificate of occupancy. For all other structures or premises, when the code official has reasonable cause to believe that a code violation exists, the code official is authorized to enter the structure or premises at reasonable times to inspect subject to constitutional restrictions on unreasonable searches and seizures. If entry is refused or not obtained, the code official is authorized to pursue recourse as provided by law.”
    One more reviewed finding on this topic
    • Limited — Building, structure, and premises inspections conducted by the City of Potosi Building Commissioner under Chapter 26.
      “Inspections may be prompted on the basis of complaint or as part of a systematic inspection program directed by the Building Commissioner.”
  • Certificate of occupancyRequired

    Buildings erected or structurally altered, and proposed building or land uses, within the City of Potosi, Washington County, Missouri.

    • No building erected or structurally altered may be occupied or used until the building inspector issues a certificate of occupancy.
    • The certificate must state that the building or proposed use complies with building and health laws and ordinances and the Potosi regulations.
    • A record of certificates is kept by the building inspector; copies are furnished on request to a person with a proprietary or tenancy interest.
    • No fee is charged for a certificate of occupancy.
    • No excavation permit for a building may be issued before application for a certificate of occupancy.
    • Application must be made coincident with the building-permit application.
    • The certificate must be issued within ten days after erection or structural alteration is completed in conformity with the regulations.
    • A certificate for a legal non-conforming use must state that the use is a legal non-conforming use.

    issuance deadline: 10 days (After erection or structural alteration has been completed in conformity with the regulations.) · certificate fee: 0 USD

    “No vacant land shall be occupied or used except for agricultural uses and no building hereafter erected or structurally altered shall be occupied or used until the building inspector shall have issued a certificate of occupancy. [...] No fee shall be charged for a certificate of occupancy. No permit for excavation for any building shall be issued before application has been made for certificate of occupancy. [...] Certificate of occupancy shall be applied for coincident with the application for a building permit and shall be issued within ten (10) days after the erection or structural alteration of such building shall have been completed in conformity with the provisions of these regulations.”
    One more reviewed finding on this topic
    • Required — A building constructed as or altered into a dwelling in the City of Potosi before human habitation
      “No building constructed as or altered into a dwelling shall be occupied in whole or in part for human habitation until the issuance of a certificate by the building official that said dwelling substantially conforms in all respects to the requirements of this act. Such certificate shall be issued within 15 days after written application therefore if said dwelling at the date of such application shall be entitled thereto.”
  • Local zoningPresent (with conditions)

    Property within the incorporated limits of the City of Potosi, Washington County, Missouri.

    • The code divides the City of Potosi into eleven zoning districts.
    • District locations and boundaries are shown on the Official Zoning Map incorporated into the article.
    • The quoted provision is city-specific and does not establish zoning in unincorporated Washington County or other municipalities.

    zoning districts: 11 districts

    “The City of Potosi shall be divided into eleven (11) zoning districts, the location and boundaries of which are shown on the Official Zoning Map, which Map is incorporated in this Article by this reference.”
    One more reviewed finding on this topic
    • Present (with conditions) — Land within the City of Potosi, Washington County, Missouri.
      “The City of Potosi shall be divided into eleven (11) zoning districts, the location and boundaries of which are shown on the Official Zoning Map, which Map is incorporated in this Article by this reference.”

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 exemptions from building-permit or contractor requirements in Washington County
  • Minimum dwelling size — Minimum dwelling size requirements in Washington County, including unincorporated areas.
  • Minimum lot size — Minimum lot size requirements in Washington County, including unincorporated areas.
  • Setbacks — Building setbacks in Washington County, including unincorporated areas.
  • Lot coverage — Lot coverage requirements in Washington County, including unincorporated areas.
8 more unanswered
  • 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 Washington County, Missouri

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

Washington County scores 72/100 on the Bolthole Index, a strong county profile. Its strengths: low administrative friction for a quiet rural property and manageable long-term carry cost.

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

Washington County does not require a county building permit for a home in unincorporated areas, and it has no county-wide zoning. Onsite septic is permitted by Washington County Health Department. 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 Washington County, Missouri?

Land in Washington County runs about $2,926 per acre, based on the latest county data.

What is the water situation in Washington County?

Washington County gets about 45.6" of rain a year, with severe drought in roughly 5.5% of years.

How remote is Washington County?

A representative private-land location has about 10,317 people within a 30-minute drive and 1,995,254 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 Washington compares in Missouri

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