California went from 27 Counties as it became a State to 58 Counties in 1909
where it remains today in 2001.
The colors match County for County but you can see how they fractured off into
other Counties. A dramatic example would be if your were looking for a
particular place located in Mariposa County (23) of 1850 and were trying to
apply the geographical boundary of 2001, this would be very misleading. There is
talk in a few Counties right now about future boundary splits. There has also
been talk for years about splitting California into two States, North and South,
but that seems unlikely for now.
| 1 | Alameda | 2 | Alpine | 3 | Amador | 4 | Butte |
| 5 | Calaveras | 6 | Colusa | 7 | Contra Costa | 8 | Del Norte |
| 9 | El Dorado | 10 | Fresno | 11 | Glenn | 12 | Humboldt |
| 13 | Imperial | 14 | Inyo | 15 | Kern | 16 | Kings |
| 17 | Klamath (1851-1874) | 18 | Lake | 19 | Lassen | 20 | Los Angeles |
| 21 | Madera | 22 | Marin | 23 | Mariposa | 24 | Mendocino |
| 25 | Merced | 26 | Modoc | 27 | Mono | 28 | Monterey |
| 29 | Napa | 30 | Nevada | 31 | Orange | 32 | Placer |
| 33 | Plumas | 34 | Riverside | 35 | Sacramento | 36 | San Benito |
| 37 | San Bernardino | 38 | San Diego | 39 | San Francisco | 40 | San Joaquin |
| 41 | San Luis Obispo | 42 | San Mateo | 43 | Santa Barbara | 44 | Santa Clara |
| 45 | Santa Cruz | 46 | Shasta | 47 | Sierra | 48 | Siskiyou |
| 49 | Solano | 50 | Sonoma | 51 | Stanislaus | 52 | Sutter |
| 53 | Tehama | 54 | Trinity | 55 | Tulare | 56 | Tuolumne |
| 57 | Ventura | 58 | Yolo | 59 | Yuba |