St. Louis County, MO Environmental Rules: Flood Zones (2026)

St. Louis County's floodplain management ordinance is found at Title X, Chapter 1008 SLCRO 1974. The ordinance was adopted to comply with the National Flood Insurance Program (44 CFR Parts 59-60) administered by FEMA, and is enforced through the St. Louis County Department of Public Works. The County applies a 1-foot freeboard standard, exceeding the FEMA minimum requirement. For new or substantially improved residential structures within Special Flood Hazard Areas (SFHAs - generally Zone A, AE, AH, AO, A99, V, or VE on Flood Insurance Rate Maps), the building permit is conditioned on the lowest floor (including basement) being elevated to a minimum of 1 foot above the Base Flood Elevation. For new or substantially improved non-residential structures, the lowest floor (including basement) must be elevated to a minimum of 1 foot above BFE, or the structure (and attendant utilities and sanitary facilities) must be floodproofed to 1 foot above BFE. New non-residential structures less than 2,000 square feet have specific elevation/floodproofing requirements at 1 foot above BFE. A Floodplain Development Permit is required from St. Louis County Public Works before any construction, substantial improvement, fill, grading, or other development in a mapped floodplain. The county uses the FEMA Flood Insurance Rate Maps (FIRMs) effective February 4, 2015 (as amended through Letters of Map Revision). St. Louis County sits at the confluence of the Mississippi River and Missouri River, with substantial floodplain along both. Major historic floods include the Great Flood of 1993 (Mississippi crested at 49.58 ft at St. Louis on August 1, 1993 - the highest gauge reading in 228 years; floodwaters were nearly 20 ft above flood stage; Mississippi remained above flood stage at St. Louis for 144 days from April 1-September 30, 1993; over 10,000 homes destroyed and 40,000 damaged regionally; total damage exceeded $12 billion). The 2017 spring flood and 2019 Missouri River flood also caused significant damage. State law (RSMo Chapter 256) sets out the Missouri State Emergency Management Agency's role in coordinating floodplain management. RSMo Chapter 644 governs water pollution and the Missouri Clean Water Law administered by the Missouri Department of Natural Resources.