Contra Costa County is a suburban county in the San Francisco Bay Area in California. As of 2000, it had a population of 948,816. The county seat is Martinez. Contra Costa was one of the original counties of California, created in 1850 and its Spanish name means opposite coast, because of its location opposite San Francisco, on San Francisco Bay. The county has a total area of 802 miČ and 90% of it is land and 10% of it is water. The most notable natural landmark in the county is 3,849' Mount Diablo, the centerpiece of Mt. Diablo State Park created legislatively in 1921. Mt. Diablo was the birthplace of the world according to local Indian tradition.