How much flood risk does Contra Costa County actually carry?
Contra Costa County lands at the 99.5th percentile of FEMA's National Risk Index for flooding, "Very High" territory — among the highest flood hazard in the country — with the hazard driven by inland rivers and flash flooding rather than the coast — FEMA's model puts a flood event here at about 1.2 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.
Contra Costa County's flood-insurance compliance gap
Out of 7,128 homes FEMA counts inside Contra Costa County's mapped flood zone, 1,997 carry the flood policy federal law requires there — 28% compliance, short of full coverage. Across all residential structures in Contra Costa County, not just the ones FEMA mandates, 0.9% carry an NFIP policy — most flood damage nationally happens outside the mapped high-risk zone, so that broader number matters too.
How Contra Costa County compares nationally
Contra Costa County sits at rank 19 of 3144 counties on FEMA's flood hazard scale (1 is worst) and rank 41 of 3144 by population (1 is biggest). About 1,172,607 people live in Contra Costa County, California, spread over 716.901 square miles.
Your street may differ from Contra Costa County's average
FEMA counts 310,943 residential structures in Contra Costa County overall, 2,681 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 Contra Costa 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.