Hillsborough Neighborhoods by Their Lots: Lot Sizes, Flood Zones and Fire Zones

San Mateo County’s public parcel layer gives an outline and a property use code for every parcel. We took the 3,852 parcels with the county’s single-family use code, 1,500 square feet or more, inside our six Hillsborough neighborhood guides, measured each lot from its outline, checked its center against FEMA’s flood map and checked each lot against CAL FIRE’s fire hazard severity zone maps. The layer has no year built, house size or city-limit line, so this post covers our six guides rather than the city as a whole. Parcel outlines downloaded October 2026; the county’s use codes were last updated in June 2020. There are no addresses or owner details here.

The short answer

• Across our six Hillsborough guides, the median single-family lot is 24,070 sq ft. That’s a little over half an acre.
• Largest lots: Tobin Clark Estates (26,080 sq ft), Skyfarm & Oaksbridge (25,220 sq ft) and Lakeview & Crystal Springs (24,310 sq ft).
• Smallest: Ryan Tract, Homeplace & Brewer (22,840 sq ft), Carolands (23,220 sq ft) and Hillsborough Park & Hillsborough Knolls (23,850 sq ft).
• Flood zones: one of the 3,852 lots has its parcel center in a FEMA high-risk flood zone (zone AE), in Hillsborough Park & Hillsborough Knolls.
• Fire zones: 1,013 lots (26%) are at least partly in a CAL FIRE fire hazard severity zone: 349 High and 664 Moderate; none are Very High. The most are in Lakeview & Crystal Springs (422) and Carolands (197).

Neighborhood by neighborhood

Largest median lot first. “Single-family lots” counts parcels with the county’s single-family use code whose center falls inside each guide’s outline; no lot falls in two guides. Each name opens its guide.

What stands out

• Median lots run from 22,840 sq ft to 26,080 sq ft: smallest in Ryan Tract, Homeplace & Brewer, largest in Tobin Clark Estates.
• The most fire-zone lots are in Lakeview & Crystal Springs: 422 of its 513 lots (82%) touch one, 167 of them High.

What the flood zones mean

• Zone AE: a 1%-a-year chance of flooding, with a base flood elevation set.
• Zone X: moderate to minimal risk, outside the 1%-a-year floodplain.
• Insurance: if the house itself is in an A or V zone, lenders on federally backed mortgages require flood insurance; a flood zone determination for the address settles it. In zone X it’s optional.

Fire hazard zones, neighborhood by neighborhood

CAL FIRE maps how severe the wildfire hazard is across California, in three classes: Moderate, High and Very High. Single-family lots inside each guide’s outline, by the highest zone that touches any part of the lot; most severe first. No lot touches a Very High zone. The other guide has none in any zone.

What the fire zones mean

• Hazard, not risk. CAL FIRE’s Office of the State Fire Marshal says the maps describe hazard: the physical conditions, like vegetation, terrain, fire history, embers and typical fire weather, over 30 to 50 years. They don’t count home hardening, defensible space or fuel reduction, which change the risk to a particular home (OSFM).
• Two kinds of map. Inside city limits (Local Responsibility Areas) we used CAL FIRE’s 2025 map; where the state is responsible for wildfire protection (State Responsibility Areas), its State Responsibility Area map. Land outside the three classes is shown as non-wildland or unzoned (OSFM).
• What a zone can bring. Depending on the zone and the kind of area, stricter building standards for new construction and additions, defensible-space rules, and a line on the seller’s natural hazard disclosure. The town’s building department can say which apply.

Reading it right

• A use code isn’t a zoning district. We counted parcels the county codes as single-family residences, 1,500 square feet or more; the codes date from June 2020, so a few newer houses may be missing or coded otherwise, and townhomes and condos aren’t counted.
• Lot sizes are measured from the county’s parcel outlines, so they can differ from a survey by a few percent.
• We checked the center of each lot against FEMA’s National Flood Hazard Layer. A lot can straddle two zones, and maps change, so check the current FEMA map for the exact address.
• The flood zone covers the land, not the house. A house can sit above the base flood elevation even in a high-risk zone. An elevation certificate settles it and can lower the insurance price.
• The fire zone describes the land around a house, not how the house is built or how the lot is kept. CAL FIRE’s zone viewer shows any parcel, and a seller’s natural hazard disclosure report states the zones for that property.
• A median isn’t a verdict. It describes the lots, not which neighborhood is right for you.

Go deeper

Hillsborough Housing Market by the Numbers covers prices and bidding, Hillsborough Home Prices by Neighborhood compares five years of house sales guide by guide, and The Most Expensive Streets in Burlingame & Hillsborough goes street by street. Flood & Fire Zones by Neighborhood compares every guide we write, and the Hillsborough city guide links every neighborhood guide.

More on Hillsborough: home prices by neighborhood · Hillsborough housing market by the numbers · the most expensive streets in Burlingame and Hillsborough · Hillsborough city guide

Buying, selling or rebuilding in a flood or fire zone?

A Property Nerd can pull the zoning, the lot, the flood and fire zones, any elevation certificate and the recent sales on your street before you write an offer, set a price or plan a rebuild. Call (408) 373-1660 or (650) 383-8606, or book a strategy call. Commissions are negotiable, and we offer bundled services, so ask us what’s included.