Two separate FEMA numbers, not one

Every county page reports two genuinely different things: a flood hazard score from FEMA's National Risk Index (how likely and severe flooding is here, physically), and a flood insurance compliance figure from NFIP policy records (whether people FEMA already requires to carry a policy actually do). Los Angeles County, CA shows how these can move independently — a very high hazard score doesn't automatically mean high compliance.

The hazard score, and how inland differs from coastal

FEMA's National Risk Index scores each county separately for inland (riverine) flood hazard and coastal storm-surge hazard, both already expressed as a 0–100 national percentile — confirmed against the full dataset (median 50.0 across 3144 counties), not a raw scale this site re-normalizes. Where a county has both scores within 10 points of each other, this site reports the hazard as "both" rather than picking one arbitrarily; Los Angeles County, CA and Bergen County, NJ are both counties where inland and coastal risk are close enough to count equally. See the coastal vs. inland guide for what that split actually means.

The Special Flood Hazard Area and mandatory insurance

Federal law requires flood insurance on any federally backed mortgage for a property inside a mapped Special Flood Hazard Area (SFHA) — FEMA's high-risk zone. FEMA's NfipResidentialPenetrationRates dataset reports, per county, what share of the residential structures inside that zone actually carry a policy. The SFHA guide covers what that zone means and why the rule exists.

Where the compliance number breaks down

FEMA's own structure-count denominator for the mapped zone is missing for roughly a quarter of US counties, and produces a compliance rate over 100% for a few dozen more where the denominator itself is wrong. This site flags both cases rather than clipping them to look normal — full detail in the data quality guide.

Where the raw numbers come from

Flood hazard scores are FEMA's National Risk Index (county table, public Esri FeatureServer). Insurance uptake is FEMA's NfipResidentialPenetrationRates (OpenFEMA). County names, coordinates, and land area come from the Census Bureau's 2025 county gazetteer, and population from Census population estimates (POPESTIMATE2024). Every source is cited on the county page it feeds.