St. Louis Region
The Mississippi and Meramec set flood limits
Jefferson County fronts the Mississippi and is crossed by the lower Meramec, both with flood history, so flood-zone status is a key question near the water.
Jefferson County has two big river questions, not one. The Mississippi marks the eastern edge, while the lower Meramec runs through the north near Arnold and Kimmswick. A parcel near either river needs an early floodplain check.
FEMA flood maps are the address-level starting point. A flood-zone designation can affect insurance expectations, lender requirements, building plans, and how a buyer reads a low-lying lot. Jefferson County also points residents to FEMA flood-map materials, so the county and federal layers belong in the same conversation.
Do the lookup before treating a river-area parcel like ordinary ground. In north county, remember that the Meramec can be the driver even when the Mississippi is the famous name on the map.
References
Where this fits: this note belongs to Jefferson County. See every local note for the county on its page.