1850 Counties of California
| County | Description | Area in sq miles | Courts held at | Pop in 1850 |
| Butte | central part, eastern side of Sacramento river | blank | Butte | 2,016 |
| Calaveras | no description | blank | blank | 16,884 |
| Colosi or Colusi | not listed | Monroeville | ||
| Contra Costa | not listed | |||
| El Dorado | no description | blank | blank | 6,842 |
| Los Angelos | south eastern boundary, on the Pacific ocean | blank | Los Angelos | 3,530 |
| Marin | on the coast, north of San Francisco bay | not listed | San Rafael | 1,036 |
| Mariposa | east side of Sierra Nevada Mts, with parallel of 38° for its northern boundary | not listed | Aqua Fria | 8,969 |
| Monterey | western part on Pacific ocean | blank | Monterey | 2,728 |
| Napa | western part | blank | Napa | 2,116 (in 1852) |
| Nevada | northeastern part, on western slope of Sierra Nevada, center of gold-quartz mining | blank | Nevada city | 21,365 |
| Sacramento | central part, Sacramento river on west | blank | Sacramento | 12,589 (in 1852) |
| San Diego | southwest corner, Pacific ocean on west | blank | San Diego | 3,530 |
| San Francisco | western boundary, Pacific ocean on west, San Francisco bay on northeast | blank | San Francisco | 36,151 |
| San Joaquin | central part, crossed by San Joaquin river | blank | Stockton | 5,929 (in 1852) |
| San Luis Obispo | western boundary, extending from the summit of the coast range of mountains to the Pacific ocean, crossed by Nacimiento & Monterey rivers | blank | San Luis Obispo | 984 (in 1852) |
| Santa Barbara | on southwest boundary, Pacific ocean on west | blank | Santa Barbara | 2,131 (in 1852) |
| Santa Clara | in west part, with San Francisco bay on northwest | blank | San Jose | 6,664 (in 1852) |
| Santa Cruz | no description | blank | Santa Cruz | 1,219 (in 1852) |
| Shasta | in northeast corner, crossed by tributaries of Sacramento river | blank | Reading's Ranch | 4,050 |
| Sierra | blank | not listed | not listed | 4,855 (in 1852) |
| Sisiyou | blank | not listed | not listed | 2,242 (in 1852) |
| Solano | in west part, Rio Sacramento river on south & east | blank | Benicia | 2,835 (in 1852) |
| Sonoma | western part, San Pablo bay on south | blank | Sonoma | 2,337 (in 1852) |
| Sutter | in northern part, crossed by Sacramento, American & Feather rivers, Honcut & Bear creeks | blank | Oro | 1,207 (in 1852) |
| Trinity | northwest corner, Pacific ocean western & summit of Coast Range of mountains as its eastern boundaries, crossed by Smith's river | blank | blank | 1,764 (in 1852) |
| Tulare | toward southern part, between Coast Range & Sierra Nevada mountains, crossed by tributaries of San Joaquin river | blank | blank | 8,575 (in 1852) |
| Tuolumne | central part, in valley of San Joaquin, between Coast Range & Sierra Nevada mountains, crossed by San Joaquin river | blank | Sonora | 17,657 |
| Yolo | central part, extending from the summit of the Coast Range of mountains to the Sacramento river | blank | Fremont | 1,307 (in 1852) |
| Yuba | northeast part, crossed by Feather, Yuba & American rivers, Honcut & Bear creeks | blank | Marysville | 22,005 (in 1852) |