San Mateo County, CA

The USDA Economic Research Service Food Access Research Atlas flags 36 of San Mateo County's 189 census tracts as low-access, covering 116,155 residents of a 754K total population. That translates to a county-wide low food access share of 15.4%, which measures how many people live more than one mile from the nearest supermarket in urban settings or more than ten miles in rural settings. Because California classifies tracts using the same distance thresholds the USDA applies nationwide, San Mateo County's figure is directly comparable to peer counties and to the state benchmark.

The food desert signal strengthens when distance is stacked with income. In San Mateo County, 26,104 residents are flagged as low-income and more than one mile from a supermarket (the urban threshold), while 8,701 meet the low-income, ten-mile rural threshold. Those overlapping conditions are the precise combination the USDA uses to designate a food desert tract. Layered context includes a median household income of $149,907, a poverty rate of 6.4%, and SNAP participation covering 10,351 households — roughly 3.9% of the county — drawn from the Census Bureau American Community Survey five-year estimates.

Transportation is the hidden variable behind most food access gaps. About 5.6% of San Mateo County households report no vehicle available, meaning any measured distance to a supermarket translates into a real trip on foot, by transit, or by asking for a ride. Group quarters residents — 1.6% of the population — are counted separately because their food access patterns follow an institution rather than a household. The county's low-access share sits near or below the typical U.S. county, but tract-level variation can still produce pockets of food desert conditions inside otherwise well-served areas.