Building permits, zoning and land rules in St. Charles County, Missouri

At a glance

Building permit

Required for residential construction in unincorporated areas⁷

Zoning

Yes, for unincorporated areas⁸

Septic

County permit required for installation, alteration, expansion or repair, with narrow maintenance exceptions⁹

RV living

Temporary only in specified locations; permit required and limited to 180 days per year⁶

Tiny home

No specific tiny-home rule confirmed; building and zoning rules still apply¹⁰¹¹

Agricultural District home size

At least 800 square feet of living space for a single-family dwelling¹²

Agricultural District lot size

Generally at least 5 acres and 150 feet wide, subject to stated exceptions¹³

Private well work

Installers generally need state permits; landowners may install their own well or pump without one¹⁴

Who to call

Contact details are copied from each office’s official page and were checked against it on October 13, 2026.

Do you need a building permit in St. Charles County, Missouri?

Yes. Unincorporated St. Charles County requires a residential building permit for projects such as detached single-family homes, mobile home installations and modular homes, with applications submitted through the Citizenserve portal¹. Like most counties around it in Missouri, St. Charles County requires a county building permit¹⁰. County-administered construction follows the 2021 I-Codes and 2020 National Electric Code with amendments¹⁵. Submit contractor information, building plans, a plot plan and estimated construction cost; review typically takes about 10 working days¹⁶. At least one inspection is required, and the permit card identifies the inspections for the job¹⁷. The residential building permit fee is the greater of a $60 minimum or 0.0073 times estimated construction cost; floodplain, land-disturbance and other fees can be added, and a $40 reinspection fee applies after three inspections¹⁸. Property inside incorporated Weldon Spring needs a land-use permit from that town instead¹. An agricultural land-use permit exception covers qualifying construction, alteration, repair and regrading under 5,000 square feet, but it does not establish an exemption from building, septic or floodplain permits¹⁹. An owner-builder exemption could not be confirmed, so ask Building and Code Enforcement before planning do-it-yourself work²⁰²¹.

Who is the St. Charles County building department, and how do you reach it?

The St. Charles County Building and Code Enforcement Division handles residential building permits in county-administered areas; call 636-949-7345, email bce@sccmo.org, or visit 201 N. Second St., Suite 412, St. Charles, Missouri²¹. The Planning & Zoning Division answers parcel-specific zoning questions at 636-949-7335 or planning@sccmo.org from Suite 420 at the same address²². Building and Code Enforcement also handles county septic and floodplain permits⁵²³. The Highway Department handles work in county-controlled or county-maintained road right-of-way at 636-949-7305 or highway@sccmo.org²⁴²⁵. Inside the City of Saint Charles, the city's own Community Development department administers zoning under Chapter 400 of its Municipal Code³. Inside Foristell, the city adopts and administers its own zoning, while septic permits for Foristell addresses still come from St. Charles County⁴²⁶.

Does St. Charles County have zoning?

Yes. St. Charles County administers zoning in unincorporated areas under Chapter 405 of its Unified Development Ordinance and the county zoning map, and has used zoning since 1959². Incorporated cities run their own: the City of Saint Charles zones under Chapter 400 of its Municipal Code³, and Foristell adopts its own zoning regulations⁴. The county rules below apply only to unincorporated land. The county zoning map and GIS show parcel-level districts, so confirm the district with Planning & Zoning before designing a house or dividing land²⁷²². In the A Agricultural District, a single-family dwelling needs at least 800 square feet of living space¹². A Agricultural lots generally need 5 acres and 150 feet of width, subject to ordinance exceptions¹³. Principal structures in that district generally have 50-foot front and rear yards and 40-foot side yards, with different standards for certain small lots and other stated conditions²⁸. Land divisions into lots of at least 5 acres in A, R or RR districts outside existing subdivisions may use a minor subdivision plat; other divisions require preliminary and final plats²⁹. Lot coverage and building height remain parcel-specific questions for Planning & Zoning²².

How do septic permits work in St. Charles County?

The St. Charles County Building and Code Enforcement Division regulates onsite wastewater treatment systems in unincorporated St. Charles County and contracting jurisdictions⁵. A county septic permit is required to install, alter, expand or repair a system, except for specified filter work, pressure adjustments and like-equipment replacements⁹. The residential minimum fee is $150, and a private sewage disposal operating permit is listed at $75¹⁸. Septic permits cover every address the county serves, including Foristell²⁶. Sanitary waste must use public sewer where applicable or an onsite system where public sewer is unavailable³⁰. Only about 3.9% of county soils rate without severe limitations for a conventional drain field, so establish septic feasibility before fixing the house location³¹. Missouri guidance says some single-family lots may be exempt from the state process, but St. Charles County has its own local permit rule for county-administered land³²⁹. The county identifies inspections at transfer of ownership but does not establish a universal inspection interval for every onsite system³³.

Can you live in an RV or tiny home on your land in St. Charles County?

St. Charles County does not allow an RV as unrestricted permanent housing under the reviewed rule. Temporary recreational shelter is allowed only on a parcel or in a subdivision platted before January 1, 1973 in the PR or A districts, or within a campground, and requires a Planning and Zoning permit⁶. RV occupancy is limited to 180 days per calendar year and one RV per parcel outside an approved campground or travel trailer park⁶. The RV must be highway-ready and have approved water, sewage and power arrangements⁶. A specific tiny-home occupancy rule could not be confirmed; a tiny home used as a dwelling still faces county building-permit and zoning review¹⁰¹¹. Off-grid living does not bypass sanitation rules because an approved onsite system is still required where public sewer is unavailable³⁴.

Building a home in St. Charles County: the steps, in order

1. Confirm that the parcel is unincorporated, identify its zoning district and obtain the applicable standards from Planning & Zoning⁸²².
2. Determine whether public sewer serves the site; otherwise establish onsite wastewater feasibility and obtain the county septic permit before locating the house³⁰⁹.
3. Check the regulated floodplain; covered development needs a separate floodplain permit, and qualifying construction must place the lowest finished floor at least 1 foot above base flood elevation³⁵.
4. Secure access; driveway work in county road right-of-way needs an advance county Special Use Permit, while a state highway entrance needs a MoDOT permit²⁴.
5. Submit contractor information, plans, a plot plan and estimated cost through Citizenserve³⁶.
6. Complete the inspections listed on the permit card¹⁷.

What should you check before buying land in St. Charles County?

Put septic feasibility near the top of due diligence because only about 3.9% of St. Charles County soils rate without severe limitations for a conventional drain field³¹. Confirm the zoning district before relying on an advertised dwelling type, setback, RV use or subdivision plan²⁷²². Check mapped flood hazards because construction, improvements, demolition and earthmoving in regulated areas can require a floodplain permit even when no building permit is required, and a floodplain permit taken separately from a building permit is effective for 2 years³⁷. Verify whether the road is county- or state-controlled before designing access because the issuing authority changes with the right-of-way²⁴. Budget beyond the purchase price: the median property-tax bill is about $3,340 a year at an effective rate near 1.1%, while typical home insurance is about $2,072 a year³⁸³⁹⁴⁰. The complete private-well permit process could not be confirmed, so ask Building and Code Enforcement which water approvals apply to the parcel²¹.

Watch-outs

• An agricultural land-use exception is not a blanket exemption from building, septic or floodplain permits¹⁹.
• RV shelter requires a temporary permit and is limited by district, plat date, duration, utilities and vehicle condition⁶.
• For a one- or two-family home, townhome, manufactured home or mobile home, an occupancy permit is specifically required to reoccupy a structure previously deemed uninhabitable⁴¹.
• Floodplain development permits can be required even where a building permit is not required⁴².

Sources

1. Residential Building Permit, quoted and re-checked
2. Unified Development Ordinance, quoted and re-checked
3. Community Development - Planning and Zoning Division FAQ, quoted and re-checked
4. Foristell: City of Foristell, MO Code of Ordinances (St. Charles County), quoted and re-checked
5. Onsite Wastewater Treatment Systems, quoted and re-checked
6. Section 405.420 Additional Vehicle Requirements, quoted and re-checked
7. Residential Building Permit, quoted and re-checked
8. Unified Development Ordinance, quoted and re-checked
9. OWTS Permitting and Inspection, quoted and re-checked
10. Residential Building Permit (2026 county census)
11. Unified Development Ordinance (2026 county census)
12. Section 405.080 A Agricultural District, quoted and re-checked
13. Section 405.080 A Agricultural District, quoted and re-checked
14. Water Wells - PUB2945 (Missouri statewide rule), quoted and re-checked
15. Building and Construction Codes, quoted and re-checked
16. Residential Building Permit, quoted and re-checked
17. Residential Building Permit, quoted and re-checked
18. St. Charles County Building Division Fees, quoted and re-checked
19. Permits, quoted and re-checked
20. (2026 county census)
21. St. Charles County Building and Code Enforcement Division (sccmo.org)
22. St. Charles County Planning & Zoning Division (sccmo.org)
23. St. Charles County Building and Code Enforcement Division (sccmo.org)
24. Working in County Right-of-Way, quoted and re-checked
25. St. Charles County Highway Department (sccmo.org)
26. Foristell: Chapter 710: Public and Private Sewers (St. Charles County), quoted and re-checked
27. Unified Development Ordinance, quoted and re-checked
28. Section 405.080 A Agricultural District, quoted and re-checked
29. St. Charles County Frequently Asked Questions, quoted and re-checked
30. Onsite Wastewater Treatment Systems (OWTS), quoted and re-checked
31. 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
32. OWTS Construction Permit Process (Missouri statewide rule), quoted and re-checked
33. Onsite Wastewater Treatment Systems (OWTS), quoted and re-checked
34. Onsite Wastewater Treatment Systems (OWTS), quoted and re-checked
35. Floodplain Development Permit, quoted and re-checked
36. Residential Building Permit, quoted and re-checked
37. Floodplain Development Permit, quoted and re-checked
38. Median property tax bill: Bolthole Index county data
39. Effective property tax rate: Bolthole Index county data
40. Typical home insurance premium: Bolthole Index county data
41. Occupancy Permit, quoted and re-checked
42. Floodplain Development Permit, quoted and re-checked

Written October 13, 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.