How much flood risk does Grundy County actually carry?
Grundy County lands at the 66.5th percentile of FEMA's National Risk Index for flooding, "Relatively Low" territory — below the national norm for flood hazard — with the hazard driven by inland rivers and flash flooding rather than the coast — FEMA's model puts a flood event here at about 1.3 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
16.6% of the homes FEMA requires to carry flood insurance in Grundy County — those inside the mapped Special Flood Hazard Area — actually have a policy in force: 120 policies against 723 mandated structures, which means a meaningful share of legally-required coverage simply isn't there. Across all residential structures in Grundy County, not just the ones FEMA mandates, 0.8% carry an NFIP policy — most flood damage nationally happens outside the mapped high-risk zone, so that broader number matters too.
Where Grundy County ranks
Grundy County sits at rank 1099 of 3144 counties on FEMA's flood hazard scale (1 is worst) and rank 965 of 3144 by population (1 is biggest). About 53,835 people live in Grundy County, Illinois, spread over 418.133 square miles.
What to do next if you own or are buying in Grundy County
Across all of Grundy County's 20,506 residential structures, 161 carry an NFIP policy today — a county-wide count that still can't tell you one address's own mapped zone.
More on how this number was built
The methodology guide shows exactly which FEMA and Census tables feed Grundy 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.