In prehistoric times, parts of the landforms in the county today were highly covered with many extinct mammals. The northern part was filled with significant deposits of sand and coal formed in the geologic areas. Contra Costa is an accumulation of different geological terranes from other parts of the world. The early settlers of the region were hunters and gatherers. The early traders from different areas invaded the area leading to the assimilation of other cultures.
The current cultural knowledge held in the area comes from the interaction of the early inhabitants and the traders. The early exchange of the Native Americans with Europeans came along with the Spanish colonization by creating missions in California. The Spanish influence in Contra Costa was direct and extensive as it led to the formation of land grants.
The county seat lies in Martinez, the largest city in the county. After the county’s formation, its southern part, including all the bayside parts of opposite San Francisco and the northern parts of Santa Clara County, was given to form the current Alameda County.
After World War II, there was a Suburban living desire in the county. The desire attracted large housing developers and companies, leading to improved housing facilities and the opening of many businesses. In return, this saw a prosperous pollution increase in the area leading to the development of the current large shopping malls and improved infrastructure.

Contra Costa signifies “Opposite coast.” The county received its name because of its situation on the opposite side of San Francisco on the eastern side of San Francisco Bay. Originally, Contra Costa was among the 27 original counties of California created at the time of statehood. The county was to be referred to as Mt. Diablo County. However, the county’s incorporation led to the changing of its name.