How much flood risk does Nassau County actually carry?
Nassau County lands at the 98.4th percentile of FEMA's National Risk Index for flooding, "Very High" territory — among the highest flood hazard in the country — with the hazard split between inland river flooding (about 3.3 times a year) and coastal storm surge (about 3.8 times a year). County-wide, not parcel-specific: FEMA's real flood-zone map is queried live, never shipped as a download.
Who actually carries the flood insurance FEMA requires
Out of 35,643 homes FEMA counts inside Nassau County's mapped flood zone, 27,164 carry the flood policy federal law requires there — 76.2% compliance, short of full coverage. Across all residential structures in Nassau County, not just the ones FEMA mandates, 9.7% carry an NFIP policy — most flood damage nationally happens outside the mapped high-risk zone, so that broader number matters too.
How Nassau County compares nationally
Nassau County sits at rank 57 of 3144 counties on FEMA's flood hazard scale (1 is worst) and rank 29 of 3144 by population (1 is biggest). Nassau County, New York covers 284.544 square miles and counts roughly 1,392,438 residents.
Checking a specific address in Nassau County
Across all of Nassau County's 371,341 residential structures, 35,824 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 Nassau County's numbers. Because storm surge plays a real role here, the guide to coastal vs. inland flood hazard is worth reading alongside this page.