Flood Zones in St. Charles County, MO: Confluence Risk

St. Charles County occupies the literal confluence of the Missouri and Mississippi Rivers, which is why more than 40% of the county carries flood-prone status and why the county is still running a federally funded buyout program for 2019 flood damage. Here's the flood history and the practical due diligence it points to for a specific parcel.

This page covers what's specific to St. Charles County. For the general explanation, see the national guide.

1993: a record crest and levee breaches that moved the confluence itself

The Great Flood of 1993 is the benchmark event for understanding flood risk in this county. The Mississippi River crested at St. Louis on August 1, 1993 at 49.58 feet -- the highest level in recorded history there, roughly six feet above the prior 1973 record and nearly 20 feet above flood stage. Levees broke at West Alton on July 7 (on the Mississippi side) and near St. Charles on July 16 (on the Missouri side), and with both levee systems compromised, the two rivers' floodwaters merged roughly 20 miles upstream of their normal confluence point, inundating farmland, towns, and low-lying communities across the county's northern and eastern river bottoms.

That event is the clearest illustration of why a levee-protected designation on a flood map should never be treated as a flood-proof guarantee in this county specifically: the 1993 flood didn't just approach the levees, it broke through two separate levee systems on two different rivers in the same summer. A parcel's levee protection today is only as good as that levee's current condition and FEMA accreditation status -- both of which can change over time as levees age, get recertified, or get modified.

2019: roughly 90,000 acres affected, and a buyout program still running

A more recent flood in 2019 affected an estimated 90,000-plus acres across St. Charles County, prompting the county to secure a $15.7 million federal hazard-mitigation grant to fund a Local Voluntary Buyout Program -- paying to acquire and demolish flood-damaged homes rather than rebuild them in place, with the resulting land converted to open space that only a government entity can own going forward. In spring 2024, the county sent eligibility letters to 947 residential property owners; as of a February 2025 update, 168 property owners had responded to that invitation and 45 applications were actively moving through the acceptance process, with the program capped at no more than 100 completed buyouts under the current grant.

For a buyer looking at land or a home in the county's flood-prone areas -- particularly northern St. Charles County near West Alton and the Mississippi, or low-lying tracts along the Missouri River bottom -- the buyout program is itself useful market information: it signals which specific areas the county and FEMA have identified as repetitive-loss or high-risk enough to justify permanent land-use conversion rather than repeated rebuilding. Ask the county's Planning & Zoning Division directly whether a specific parcel or neighborhood has been part of buyout discussions, since that history can affect both insurability and long-term value even for a property that wasn't itself bought out.

Before you build or buy: what to actually verify

A floodplain development permit in St. Charles County is a separate requirement from a standard building permit, issued through the Planning & Zoning Division, and it applies on top of whatever zoning approvals a project already needs. Because the county's flood-zone maps get revised periodically and levee accreditation status can change, don't rely on an older FIRM panel or a listing description -- pull the current preliminary and effective flood maps through FEMA's Map Service Center and confirm directly with the county's floodplain administration function ((636) 949-7335) for the specific parcel's zone designation (X, AE, or otherwise) before assuming a building site is buildable as-is.

For a parcel behind an accredited levee, ask specifically which levee system protects it, whether that levee is currently accredited by FEMA, and whether any recertification or map-revision process is underway -- the same category of question that mattered in 1993, when levees that had stood for decades failed within weeks of each other. For a parcel near a river bottom without levee protection at all, budget for flood insurance as a real, ongoing cost rather than an afterthought, and factor the county's active buyout activity in nearby areas into your long-term expectations for the property's insurability and resale market.

Flood Zones in St. Charles County, Missouri

1993: a record crest and levee breaches that moved the confluence itself

2019: roughly 90,000 acres affected, and a buyout program still running

Before you build or buy: what to actually verify

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