Contra Costa County is located in the state of California and is home to 1,161,413 people. It has an area of 720 square miles (1,865 km) and is identified by the FIPS code 13. The county is accessible from San Francisco, Oakland, and Berkeley via State Route 24 and the Caldecott Tunnel. Interstate 580 connects Contra Costa to downtown Alameda County to the west and Stockton and the Central Valley to the east. Interstate 680 is the main route that connects Contra Costa to South Bay and Silicon Valley to the south, and to Sacramento to the north.
Contra Costa County is home to a plethora of parks and trails, as well as reservoirs. It is also home to museums managed by the East Bay Regional Park System, the East Bay MUD (the Municipal Public Services District is the local water supply company) and areas designated as open spaces. There are no major airports in Contra Costa County with regular passenger service, although there are several general aviation airports. The same hills that keep Contra Costa culturally isolated also protect it from a climate point of view; the area is usually 5 to 10 °C (10 to 20 °F) warmer than the bay in summer.
Contra Costa County has a total of 58 counties.