How much flood risk does Johnson County actually carry?
Johnson County lands at the 37.9th 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 once every 1 years. This describes the county, not any one street — FEMA only publishes exact parcel zones through a live map service.
Mandatory flood insurance compliance in Johnson County
Johnson 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 Johnson County, not just the ones FEMA mandates, 0.1% carry an NFIP policy — most flood damage nationally happens outside the mapped high-risk zone, so that broader number matters too.
Where Johnson County ranks
Johnson County sits at rank 2018 of 3144 counties on FEMA's flood hazard scale (1 is worst) and rank 2203 of 3144 by population (1 is biggest). About 13,320 people live in Johnson County, Illinois, spread over 343.737 square miles.
What to do next if you own or are buying in Johnson County
FEMA counts 5,587 residential structures in Johnson County overall, 5 of them carrying some form of NFIP coverage — but a lender or insurer cares about one parcel, not that county total.
More on how this number was built
The methodology guide shows exactly which FEMA and Census tables feed Johnson County's numbers. See the data quality guide for why Johnson County, like hundreds of other counties, doesn't get a clean compliance percentage.