The U.S. state of California is divided into 58 counties. Counties are responsible for local services and law enforcement for areas within their borders that are not within incorporated cites, as well as providing local-level courtss.
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 El Dorado, Fremont Yola, Mt. Diablo Contra Costa, San Jose Santa Clara, Oro Tuolumne, and Redding 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.
Klamath County was created in 1851 from the northern half of Trinity County, but in 1874 it was divided between Humboldt and Siskiyou counties.
Pautah County was created in 1852 out of territory which, the state of California assumed, was to be ceded to it by the United States Congress from territory in what is now the state of Nevada. When the cession never occurred, the state legislature officially abolished the never-created county in 1859.
Mariposa - One of the original counties. Part of the county's territory went to Tulare County in 1852, Merced in 1855, Fresno in 1856 and Mono in 1861. Mariposa County was the largest of the state's original counties, but territory that was once part of Mariposa is now in the counties of 12 other counties -- Fresno, Inyo, Kern, Kings, Los Angeles, Madera, Merced, Mono, San Benito, San Bernardino, San Luis Obispo, and Tulare.
Mendocino - One of the original counties.
1855 - Merced, from parts of Mariposa. Part of the county's territory went to Fresno in 1856
1855 - Modoc, from parts of Siskiyou
1861 - Mono, from parts of Calaveras, Fresno and Mariposa. Part of the county's territory went to Inyo in 1866
Monterey - One of the original counties. Part of the county's territory went to San Benito in 1874
Napa - One of the original counties. Part of the county's territory went to Lake in 1861