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California Counties
The U.S. state of California is divided into fifty-eight counties. On January 4, 1850, the California constitutional committee recommended the formation of 18 counties. They were Benicia, Butte, Fremont, Los Angeles, Mariposa, Monterey, Mount Diablo, Oro, Redding, Sacramento, San Diego, San Francisco, San Joaquin, San Jose, San Luis Obispo, Santa Barbara, Sonoma, and Sutter. On April 22, the Counties of Branciforte, Calaveras, Coloma, Colusi, Marin, Mendocino, Napa, Trinity, and Yuba were added. Benicia was renamed Solano, Coloma to El Dorado, Fremont to Yola, Mt. Diablo to Contra Costa, San Jose to Santa Clara, Oro to Tuolumne, and Redding to Shasta. One of the first state legislative acts regarding Counties was to rename Branciforte County to Santa Cruz, Colusi to Colusa, and Yola to Yolo.

The last California county to have been established is Imperial County in 1907.

Contra Costa County, California

Contra Costa County History, Geography, and Demographics

County Seat: Martinez
Year Organized: 1850
Square Miles: 720
Court House:

651 Pine Street, 11th Floor
County Administration Building
Martinez, CA 94553-1229

Etymology - Origin of County Name

The name signifies "opposite coast," because of its situation opposite San Francisco, in an easterly direction, on San Francisco Bay. In 1853, Alameda County was formed from territory originally included in this county.


County QuickFacts: Census Bureau Quick Facts

County History

The County of Contra Costa, California (the "County") was incorporated in 1850 as one of the original 27 counties of the State of California (the "State"), with the City of Martinez as the County Seat. It is one of the nine counties in the San Francisco-Oakland Bay Area. The County is the ninth most populous county in California, with its population reaching approximately 1,051,677 as of January 1, 2008.


According to the U.S. Census Bureau, the county has a total area of 802 square miles (2,078 kmē), of which, 720 square miles (1,865 kmē) of it is land and 82 square miles (213 kmē) of it (10.25%) is water.

Neighboring Counties:

  • North: Solano County
  • Northeast: Sacramento County
  • East: San Joaquin County
  • South: Alameda County
  • West: San Francisco Bay; Marin County

Cities and Towns:

- Antioch city Incorporated Area
- Brentwood city Incorporated Area
- Clayton city Incorporated Area
- Concord city Incorporated Area
- Danville town Incorporated Area
- El Cerrito city Incorporated Area
- Hercules city Incorporated Area
- Lafayette city Incorporated Area
- Martinez (County Seat) city Incorporated Area
- Moraga town Incorporated Area
- Oakley city Incorporated Area
- Orinda city Incorporated Area
- Pinole city Incorporated Area
- Pittsburg city Incorporated Area
- Pleasant Hill city Incorporated Area
- Richmond city Incorporated Area
- San Pablo city Incorporated Area
- San Ramon city Incorporated Area
- Walnut Creek city Incorporated Area

County Resources:

Enter County Resources and Information Here

County Resources
Counties: US Map
The history of our nation was a prolonged struggle to define the relative roles and powers of our governments: federal, state, and local. And the names given the counties, our most locally based jurisdictions, reflects the "characteristic features of this country!"