Contra Costa County, California

For the California wine region, see Contra Costa AVA.

Contra Costa County
County
Mount Diablo Las Trampas Regional Wilderness Concord Moraga Carquinez Strait Richmond and San Pablo
Seal Coat of arms Wordmark
Location in the state of California
Interactive map of Contra Costa County
Country	United States
State	California
Region	Bay Area
Incorporated	February 18, 1850
Named for	"Opposite coast" (Spanish: Contra costa) of the San Francisco Bay
County seat	Martinez, California
Largest city	Concord, California (population and land area) Richmond, California (total area)
Government
• Type	Council–CAO
• Body	Board of Supervisors
• Chair	Diane Burgis
• Vice Chair	Ken Carlson
• Board of Supervisors	Supervisors John Gioia Candace Andersen Diane Burgis Ken Carlson Shanelle Scales-Preston
• County Administrator Office	Monica Nino
Area
• Total	804 sq mi (2,080 km2)
• Land	715.94 sq mi (1,854.3 km2)
• Water	81 sq mi (210 km2)
Highest elevation	3,852 ft (1,174 m)
Population  (2020 United States census)
• Total	1,165,927
• Estimate  (2025)	1,170,070
• Density	1,628.5/sq mi (628.78/km2)
GDP
• Total	$94.802 billion (2022)
Time zone	UTC−8 (Pacific Time Zone)
• Summer (DST)	UTC−7 (Pacific Daylight Time)
Area code	510, 341, 925
FIPS code	06-013
GNIS feature ID	1675903
Congressional districts	8th, 9th, 10th
Website	contracosta.ca.gov

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Contra Costa County (/ˌkɒntrə ˈkɒstə/ ^ⓘ; Contra Costa, Spanish for 'Opposite Coast') is a county located in the U.S. state of California, in the East Bay of the San Francisco Bay Area. As of the 2020 United States census, the population was 1,165,927. The county seat is Martinez. It occupies the northern portion of the East Bay region of the San Francisco Bay Area and is primarily suburban. The county's name refers to its position on the other side of the bay from San Francisco. Contra Costa County is included in the San Francisco–Oakland–Fremont, CA metropolitan statistical area and the San Jose–San Francisco–Oakland, CA combined statistical area.