San Mateo County, California

San Mateo County
Motto: 
All of California in One County
Interactive map of San Mateo County
Location in California
Coordinates: 37°26′N 122°22′W / 37.44°N 122.36°W / 37.44; -122.36
CountryUnited States
StateCalifornia
IncorporatedApril 19, 1856
Named afterSaint Matthew (English translation)
County seat
and largest city by area
Redwood City
Largest city by populationSan Mateo
Government
 • TypeCouncil–CEO
 • BodyBoard of Supervisors
 • PresidentNoelia Corzo
 • Vice PresidentRay Mueller
 • Board of Supervisors
Supervisors
 • County executive officerMike Callagy
Area
 • Total
744 sq mi (1,930 km2)
 • Land448 sq mi (1,160 km2)
 • Water293 sq mi (760 km2)
Highest elevation
2,603 ft (793 m)
Population
 • Total
764,442
 • Density1,704/sq mi (658/km2)
GDP
 • Total$202.488 billion (2023)
Time zoneUTC-8 (Pacific Time Zone)
 • Summer (DST)UTC-7 (Pacific Daylight Time)
Area codes415/628, 650
FIPS code06-081
GNIS feature ID277305
Congressional districts15th, 16th
Websitesmcgov.org

San Mateo County, officially the County of San Mateo, is a county located in the U.S. state of California. As of the 2020 United States census, the population was 764,442. Redwood City is the county seat, the third-most populated city in the county after Daly City and San Mateo.

San Mateo County is included in the San Francisco–Oakland–Berkeley, CA MSA (metropolitan statistical area), Silicon Valley, and is part of the San Francisco Bay Area, the nine counties bordering San Francisco Bay. As of 2020, it has a median household income of $128,091, the fourth-highest household income of any county in the nation behind Loudoun County, Virginia, Falls Church, Virginia, and Santa Clara County, California.

The county covers most of the San Francisco Peninsula. The county is predominantly suburban and is home to many corporate campuses.