Contra Costa County is a county in the state of California in the United States. As of the 2010 census, the population was 1,049,025. The county seat is Martinez. The name is Spanish for "opposite coast", referring to its position on the other side of the bay from San Francisco. Contra Costa County is included in the San Francisco–Oakland–Hayward, CA Metropolitan Statistical Area, CA Metropolitan Statistical Area. It occupies the northern portion of the East Bay region and is primarily suburban.