Floodplain exposure by community area
Where does Chicago’s flood risk concentrate? Search your address to see your community area, or click any area on the map. Each area is shaded by the share of its parcels in a FEMA high-risk flood zone.
How to read this map
A Special Flood Hazard Area (SFHA) is FEMA’s regulatory 1%-annual-chance floodplain — the “100-year flood” zone where flood insurance is mandatory with a federally-backed mortgage. Each community area is shaded by the share of its parcels that fall in one; the darker the fill, the more of the area is exposed. Citywide the share is small (Chicago sits mostly on high ground), so the story is where it concentrates — along the river branches and the Calumet region.
Source: the Cook County Assessor’s own per-parcel FEMA-SFHA determination (the env_flood_fema_sfha flag on the Assessor parcel universe), which reads the FEMA National Flood Hazard Layer for every parcel. We use it because FEMA’s live map service can’t reliably serve Cook’s large water-body geometries — the Assessor’s complete parcel-level flag is the better local source. It covers the high-risk SFHA only, not the lower-risk 0.2% (500-year) fringe. See methodology for details.