By John Taylor.

One hundred and fifty years ago, the first gathering of the California Legislature divided the state into 27 counties. Over the next 57 years, the state’s territory was further subdivided and county boundaries were changed to create the names and places we recognize today.

It could be said that the history of California’s counties began when the “Treaty of Peace, Friendship, Limits, and Settlement between the United States of America and the Mexican Republic” was signed on Feb. 2, 1848. The treaty ended the Mexican War and placed California under jurisdiction of the United States. Better known as the treaty of Guadalupe Hidalgo, it was named after the city, near Mexico City, where it was signed. Treaty copies were subsequently exchanged and ratified in the Mexican city of Queretaro on May 30, 1848, and the treaty was proclaimed by President James K. Polk on July 4, 1848.

California’s first constitutional convention was held in Monterey, starting in September 1849. Delegates came from ten districts: San Diego, Los Angeles, Santa Barbara, San Luis Obispo, Monterey, San Jose, Sonoma, San Francisco, San Joaquin, and Sacramento.

This constitutional convention established a committee, chaired by General Mariano Vallejo, that considered the creation of California’s first counties. On Jan. 4, 1850, the 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.


The first session of the California Legislature was held from Dec. 15, 1849, to April 22, 1850, at the City of Pueblo de San Jose. Based, in part, on further recommendations from General Vallejo’s committee, the Legislature made additions and changes to the list of 18 counties.

Nine more counties were added to the proposal-Branciforte, Calaveras, Coloma, Colusi, Marin, Mendocino, Napa, Trinity, and Yuba-bringing the total number of original counties to 27.

Before it finally adopted a statute, the state Legislature approved several name changes. Benicia was renamed Solano, Coloma became El Dorado, Fremont transformed into Yola, Mt. Diablo became Contra Costa, San Jose was renamed Santa Clara, Oro shifted to Tuolumne, and Redding became Shasta.

Following these additions and name changes, the state’s first counties were created by an Act signed Feb. 18, 1850. In summary, the first 27 counties were Butte, Branciforte, Calaveras, Colusi, Contra Costa, El Dorado, Los Angeles, Marin, Mariposa, Mendocino, Monterey, Napa, Sacramento, San Diego, San Francisco, San Joaquin, San Luis Obispo, Santa Barbara, Santa Clara, Shasta, Solano, Sonoma, Sutter, Trinity, Tuolumne, Yola, and Yuba.

Not long after the Legislature adopted its first statute creating counties, subsequent statutes changed additional county names to those now familiar to us: Branciforte to Santa Cruz, Colusi to Colusa, and Yola to Yolo.


On Sept. 9, 1850, California became one of 31 states in the union at that time. Proposals for many more counties were soon presented.

Particularly in the northern part of the state, fights arose within counties between mining districts and agricultural districts. Conflicts also developed in many counties over what community should be the county seat. Without paved roads, automobiles, and telephones, the distance from a home or business to a county seat was more important than it is now.

Some of these issues could often be partly resolved by dividing counties.In every one of the first seven years after 1850, at least one new county was created. Eighteen of the original 27 counties helped give birth to another county.


The California Legislature also created counties that are not found on today’s maps.

  • Klamath County was created in 1851 from the northern half of Trinity County’s mostly mountainous mining country. In 1857 Klamath County, in turn, lost significant territory to the newly formed Del Norte County. In 1875, as charges of corruption in the county increased, Klamath County was abolished. Its territory was divided between Humboldt and Siskiyou counties. Territory that at one time was in Klamath County is now in Del Norte, Humboldt, Siskiyou, and Trinity counties.
  • Pautah County was created in 1852 by an act that was to become effective when the United States Congress ceded to California territory in what is now Nevada. The county seat was to have been Carsonville. California never acquired the territory, and the act creating the county was repealed in 1859.
  • Los Angeles County transformed from a small county along the coast to a large county extending to the Nevada border and then back again to being a relatively small county in area, although now it has about 29 percent of the state’s population.
  • In 1850, Mariposa County was the largest in area of the original counties: It covered about a sixth of the state. It was larger than the present San Bernardino County, which is now the largest county in the country. Today’s Mariposa County is the parent or grandparent of all or parts of 12 other counties, more than produced by any other California county. Territory that at one time was in Mariposa County is now part or all of Fresno, Inyo, Kern, Kings, Los Angeles, Madera, Merced, Mono, San Benito, San Bernardino, San Luis Obispo, and Tulare Counties.


In California’s early history it was relatively easy to create a new county. You simply had to convince the state Legislature. As a result, to the original 27 counties, 33 more were added, one of which (Klamath) died and one of which (Pautah) was never in California.

Today it is much more difficult to establish a new county. In 1894 the state constitution was amended to require uniform laws concerning county creation. In Sections 23320 through 23374, the California Government Code specifies the procedure: A favorable majority vote is needed both in the entire county affected and in the territory of the new county, an almost impossible task. As a result of the tougher laws with constitutional foundation, no new county has been formed since 1907, when Imperial County was created from eastern San Diego County, although it is still theoretically possible.


In this table, the left column shows the source of the territory when each county, listed in the middle column, was created. The right column shows the destination of the territory moved from one county to another at the time of the birth of a new county.




Contra Costa, Santa Clara 1853 Alameda
Amador, El Dorado, Calaveras, Tuolumne 1864 Alpine
Calaveras, El Dorado 1854 Amador Alpine 1864
One of the original 27 counties 1850 Butte Plumas 1854; Tehama 1856
One of the original 27 counties 1850 Calaveras Amador 1854; Alpine 1864
One of the original 27 counties 1850 Colusa Tehama 1856; Glenn 1891
One of the original 27 counties 1850 Contra Costa Alameda 1853
Klamath 1857 Del Norte
One of the original 27 counties 1850 El Dorado Amador 1854; Alpine 1864
Mariposa, Merced, Tulare 1856 Fresno Mono 1861; Madera 1893
Colusa 1891 Glenn
Trinity 1853 Humboldt
San Diego 1907 Imperial
Mono, Tulare 1866 Inyo
Los Angeles, Tulare 1866 Kern
Tulare 1893 Kings
Trinity 1851 Klamath Del Norte 1857
Napa 1861 Lake
Plumas, Shasta 1864 Lassen
One of the original 27 counties 1850 Los Angeles San Bernardino 1853; Kern 1866; Orange 1889
Fresno 1893 Madera
One of the original 27 counties 1850 Marin
One of the original 27 counties 1850 Mariposa Tulare 1852; Merced 1855;
Fresno 1856; Mono 1861
One of the original 27 counties 1850 Mendocino
Mariposa 1855 Merced Fresno 1856
Siskiyou 1855 Modoc
Calaveras, Fresno, Mariposa 1861 Mono Inyo 1866
One of the original 27 counties 1850 Monterey San Benito 1874
One of the original 27 counties 1850 Napa Lake 1861
Yuba 1851 Nevada
Los Angeles 1889 Orange
Sutter and Yuba 1851 Placer
Butte 1854 Plumas Lassen 1864
One of the original 27 counties 1850 Sacramento
Monterey 1874 San Benito
Los Angeles 1853 San Bernardino Riverside 1893
One of the original 27 counties 1850 San Diego Riverside 1893; Imperial 1907
One of the original 27 counties 1850 San Francisco San Mateo 1856
One of the original 27 counties 1850 San Joaquin
One of the original 27 counties 1850 San Luis Obispo
San Francisco 1856 San Mateo
One of the original 27 counties 1850 Santa Barbara Ventura 1872
One of the original 27 counties 1850 Santa Clara Alameda 1853
One of the original 27 counties 1850 Santa Cruz
One of the original 27 counties 1850 Shasta Siskiyou 1852; Tehama 1856;
Lassen 1864
Yuba 1852 Sierra
Shasta and Klamath 1852 Siskiyou Modoc 1855
One of the original 27 counties 1850 Solano
One of the original 27 counties 1850 Sonoma
Tuolumne 1854 Stanislaus
One of the original 27 counties 1850 Sutter Placer 1851
Butte, Colusa, and Shasta 1856 Tehama
One of the original 27 counties 1850 Trinity Klamath 1852; Humboldt 1853
Mariposa 1852 Tulare Fresno 1856; Kern 1866;
Inyo 1866; Kings 1893
One of the original 27 counties 1850 Tuolumne Stanislaus 1854; Alpine 1864
Santa Barbara 1872 Ventura
One of the original 27 counties 1850 Yolo
One of the original 27 counties 1850 Yuba Placer 1851; Nevada 1851; Sierra 1852

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Originally posted at the California State Association of Counties.

John Taylor is a retired clerk of the San Francisco Board of Supervisors and a past president of the California Clerk of the Board of Supervisors Association.