Is Warren County, IL in a flood zone?
FEMA's National Risk Index puts Warren County's flood hazard at the 11th percentile nationally — among the lowest flood hazard in the country — driven by inland rivers and flash flooding rather than the coast — FEMA's model puts a flood event here at about once every 1 years. That's a county-wide figure, not a per-address one — FEMA's parcel maps are a live lookup, not a bulk file.
Who actually carries the flood insurance FEMA requires
Warren County is one of the counties where FEMA's own denominator for mandated flood-zone structures is missing, so no compliance rate is shown rather than a guessed one — the data quality guide covers how common this is. Across all residential structures in Warren County, not just the ones FEMA mandates, 0.4% carry an NFIP policy — most flood damage nationally happens outside the mapped high-risk zone, so that broader number matters too.
How Warren County compares nationally
Warren County sits at rank 2816 of 3144 counties on FEMA's flood hazard scale (1 is worst) and rank 2019 of 3144 by population (1 is biggest). Warren County, Illinois covers 542.36 square miles and counts roughly 16,217 residents.
What to do next if you own or are buying in Warren County
26 of Warren County's 6,395 residential structures carry flood coverage of some kind, per FEMA's latest count — useful context, not a substitute for checking one parcel.
More on how this number was built
The methodology guide shows exactly which FEMA and Census tables feed Warren County's numbers. See the data quality guide for why Warren County, like hundreds of other counties, doesn't get a clean compliance percentage.