St. Charles County, Missouri Building Permit Guide

By the Census Bureau’s Vintage 2025 estimates, the largest cities in St. Charles County are O’Fallon (96,101), St. Charles (72,561), St. Peters (61,479) and Wentzville (49,495). The unincorporated balance of the county had 93,693 people.

This guide covers the county’s building, land use, land disturbance, floodplain, septic and right-of-way permits, and the City of St. Charles. The county says it also issues permits in contract cities, but they are listed only in its map-based Permit Lookup Tool, so check the tool for your address.

What requires a building permit in St. Charles County?

A county residential building permit is needed for fences over six feet, retaining walls over four feet and, when electric is included, any structure regardless of size. A land use permit is required to build, alter or repair any structure or to re-grade under 5,000 sq ft; a building permit application doubles as the land use application. A floodplain development permit is needed for almost any work in the regulated floodplain, even fences, windows or reroofing that need no building permit.

Missouri has no mandatory statewide building code for private construction: a county, fire protection district or municipality may adopt one (usually by reference under RSMo 67.280), and in parts of the state none has. Building codes in Missouri

Who handles permitting in St. Charles County?

St. Charles County codes and portal

The county has adopted the 2021 I-Codes and the 2020 National Electrical Code with county amendments, including its own Private Sewage Disposal Code and Swimming Pool and Spa Code. Permits, contractor licenses and plan submittals go through the Citizenserve Citizen Access Portal.

The county warns of fraudulent wire-transfer payment requests: it never asks for wire transfers, and questions go to Community Development at 636-949-7346.

Floodplain, land disturbance and septic

More than 40% of St. Charles County is flood-prone. New or substantially improved structures in the regulated floodplain must have the lowest floor at least 1.0 feet above base flood elevation.

A land disturbance permit is required for disturbance of 5,000 sq ft or more. Individual homes and minor work under one acre usually qualify for a MINOR permit at a flat $100 fee without erosion-control plans.

Septic (onsite wastewater) permits for installing, altering, expanding or repairing a system come from the Division of Building and Code Enforcement, not a health department.

St. Charles County permit costs and fees

The building permit fee is the higher of the applicant’s and the county’s estimated construction cost (from the ICC Building Safety Journal) x 0.0073, or the minimum fee if that is higher. Minimums include $60.00 for a residential building permit and $100.00 for decks and accessory structures. Each reinspection after 3 inspections is $40.00.

Fees for local building permits are set by whichever body adopted the code; Missouri has no state fee schedule for them. Permit fees in Missouri

Building permits in the City of St. Charles

Inside the City of St. Charles, the county seat, permits come from the city’s Building Division. The city uses the 2021 IBC/IRC and 2020 NEC, requires permits for sheds over 144 square feet and fences over six feet, and may require Landmarks Board approval in the Extended Historic District. City inspections are scheduled at (636) 949-3222.

How to get a building permit in St. Charles County

Permit validity is set by the issuing office's ordinance rather than by statute, so confirm the expiry on phased or delayed work. Permit validity in Missouri

Inspections in St. Charles County

County inspections must be called in to the Community Development office at 636-949-7345 by 5 p.m. the business day before the requested date, and the permit must be posted so it is visible from the street.

Official St. Charles County permitting resources

These are the primary sources behind this guide. Codes, fee schedules and procedures change — confirm the position for your filing date.

• St. Charles County Community Development
• Residential building permit
• Mechanical/electrical/plumbing permit
• Building and construction codes
• Land use permit
• Land disturbance permit
• Floodplain development permit
• Septic (OWTS) permitting
• Working in county right-of-way
• City of St. Charles Building Division
• Census Bureau Vintage 2025 city estimates (Missouri)

Frequently asked questions

Who issues septic permits in St. Charles County?

The Division of Building and Code Enforcement, not a health department.

Does reroofing in the floodplain need a permit?

A floodplain development permit is needed for almost any work in the regulated floodplain, even reroofing that needs no building permit.

How do I book a county inspection?

Call 636-949-7345 by 5 p.m. the business day before the requested date.

Simplify St. Charles County permitting with Alliance Permitting

• Confirm whether the county or a city issues the permit for the address
• Line up floodplain, land use or land disturbance approvals before the building permit
• File in the county or city portal and book each inspection on time

Alliance Permitting is a permit documentation and submission company in Missouri. We prepare your paperwork, file it correctly and coordinate with the permitting authority through issuance. We are not a contractor and we do not perform licensed plan review or inspections; that work stays with your licensed team and the jurisdiction.

This guide is provided by Alliance Permitting for general information about St. Charles County permitting. Requirements, fees, and procedures change; confirm details with the permitting authority before relying on them.