San Mateo County, CA flood risk explained
Flood hazard in San Mateo County sits at the 98.4th national percentile, well above the national norm for flood hazard; split between inland river flooding (about 1.4 times a year) and coastal storm surge (about once every 1 years). County-wide, not parcel-specific: FEMA's real flood-zone map is queried live, never shipped as a download.
San Mateo County's flood-insurance compliance gap
Out of 7,052 homes FEMA counts inside San Mateo County's mapped flood zone, 2,178 carry the flood policy federal law requires there — 30.9% compliance, short of full coverage. Looking beyond the mandated zone, 1.8% of all residential structures in San Mateo County carry flood coverage voluntarily or otherwise — relevant because most NFIP claims nationally come from outside the mapped SFHA.
San Mateo County against the rest of the country
Among the 3144 US counties FEMA scores for flood hazard, San Mateo County ranks 58 — 1 being the highest hazard nationally — and 91 by population among all 3144 counties covered here, where 1 is the largest. San Mateo County, California covers 448.603 square miles and counts roughly 742,893 residents.
Checking a specific address in San Mateo County
FEMA counts 182,415 residential structures in San Mateo County overall, 3,346 of them carrying some form of NFIP coverage — but a lender or insurer cares about one parcel, not that county total.
Where San Mateo County's figures come from
Every figure on this page traces to a named FEMA dataset, documented in the methodology guide. San Mateo County's coastal exposure is covered in the coastal vs. inland flood risk guide, including how storm surge risk differs from river flooding.