Marin County, CA: flood risk, in FEMA's own numbers
On FEMA's National Risk Index, Marin County scores at the 97.2th percentile for flood hazard, rated "Very High" — among the highest flood hazard in the country. The hazard here is split between inland river flooding (about 2.1 times a year) and coastal storm surge (about 1.6 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.
Marin County's flood-insurance compliance gap
Homes with a federally backed mortgage inside Marin County's mapped high-risk flood zone (the Special Flood Hazard Area, or SFHA) are legally required to carry an NFIP flood policy. In practice, 38% of them do — 3,734 active policies against 9,823 structures FEMA counts in that zone, leaving a real compliance gap. Looking beyond the mandated zone, 5.4% of all residential structures in Marin County carry flood coverage voluntarily or otherwise — relevant because most NFIP claims nationally come from outside the mapped SFHA.
Where Marin County ranks
Among the 3144 US counties FEMA scores for flood hazard, Marin County ranks 100 — 1 being the highest hazard nationally — and 286 by population among all 3144 counties covered here, where 1 is the largest. About 256,400 people live in Marin County, California, spread over 520.141 square miles.
Your street may differ from Marin County's average
FEMA counts 84,609 residential structures in Marin County overall, 4,542 of them carrying some form of NFIP coverage — but a lender or insurer cares about one parcel, not that county total.
Where Marin County's figures come from
Every figure on this page traces to a named FEMA dataset, documented in the methodology guide. Marin County's coastal exposure is covered in the coastal vs. inland flood risk guide, including how storm surge risk differs from river flooding.