How much flood risk does Jefferson County actually carry?
Jefferson County lands at the 79.5th percentile of FEMA's National Risk Index for flooding, "Relatively Moderate" territory — a middling flood hazard by national standards — with the hazard driven by inland rivers and flash flooding rather than the coast — FEMA's model puts a flood event here at about 1.6 times a year. That's a county-wide figure, not a per-address one — FEMA's parcel maps are a live lookup, not a bulk file.
Jefferson County's flood-insurance compliance gap
Out of 729 homes FEMA counts inside Jefferson County's mapped flood zone, 122 carry the flood policy federal law requires there — 16.7% compliance, short of full coverage. Across all residential structures in Jefferson County, not just the ones FEMA mandates, 0.5% carry an NFIP policy — most flood damage nationally happens outside the mapped high-risk zone, so that broader number matters too.
Jefferson County against the rest of the country
Jefferson County sits at rank 674 of 3144 counties on FEMA's flood hazard scale (1 is worst) and rank 686 of 3144 by population (1 is biggest). About 86,245 people live in Jefferson County, Wisconsin, spread over 556.494 square miles.
Your street may differ from Jefferson County's average
153 of Jefferson County's 29,930 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 Jefferson County's numbers. The guide to what the Special Flood Hazard Area actually means explains why the mandatory-insurance rule exists and who it applies to.