Jefferson County, IL: flood risk, in FEMA's own numbers
On FEMA's National Risk Index, Jefferson County scores at the 59th percentile for flood hazard, rated "Relatively Low" — below the national norm for flood hazard. The hazard here is driven by inland rivers and flash flooding rather than the coast — FEMA's model puts a flood event here at about 1.5 times a year. This describes the county, not any one street — FEMA only publishes exact parcel zones through a live map service.
Who actually carries the flood insurance FEMA requires
Out of 126 homes FEMA counts inside Jefferson County's mapped flood zone, 16 carry the flood policy federal law requires there — 12.7% compliance, short of full coverage. Looking beyond the mandated zone, 0.2% of all residential structures in Jefferson County carry flood coverage voluntarily or otherwise — relevant because most NFIP claims nationally come from outside the mapped SFHA.
How Jefferson County compares nationally
Among the 3144 US counties FEMA scores for flood hazard, Jefferson County ranks 1347 — 1 being the highest hazard nationally — and 1291 by population among all 3144 counties covered here, where 1 is the largest. Jefferson County, Illinois is home to about 36,107 people across 571.237 square miles of land.
Your street may differ from Jefferson County's average
FEMA counts 12,022 residential structures in Jefferson County overall, 20 of them carrying some form of NFIP coverage — but a lender or insurer cares about one parcel, not that county total.
Where Jefferson County's figures come from
Every figure on this page traces to a named FEMA dataset, documented in the methodology guide. If you're unsure why any of this insurance requirement exists at all, the SFHA explainer covers it from first principles.