San Mateo County flood zones: who's paying more than the map requires

We analyzed every parcel touching a FEMA flood zone in San Mateo County — 36,290 of them — against current flood maps and USGS LiDAR ground elevations. Two groups stand out.

23,153 properties are mapped OUTSIDE the high-risk zone

These parcels sit outside the Special Flood Hazard Area on today's map — many moved out by levee accreditations and FEMA map revisions. Flood insurance is not federally required for them, yet owners with stale lender determinations may still be paying. If your address is one of them, the fix is paperwork: the current determination, documented for your lender.

1,225 flood-zone parcels measure ABOVE the flood elevation

These are inside the mapped zone, but LiDAR shows their ground at least a foot above the governing Base Flood Elevation — the profile of a FEMA Letter of Map Amendment candidate (a no-fee process that ends the insurance requirement; see our LOMA guide). Another 744 parcels measure within a foot — close enough that a field survey could go either way.

Counts are from our analysis of FEMA National Flood Hazard Layer polygons, county parcel data, and USGS 3DEP LiDAR (San Mateo County, 2026). Parcel-level screening, not a survey; individual results require the property-specific analysis in our reports.