California: Commentary

California Atlas of Historical County Boundaries

John H. Long, Editor; Peggy Tuck Sinko, Historical Compiler; Laura Rico-Beck, GIS Specialist and Digital Compiler; Peter Siczewicz, ArcIMS Interactive Map Designer; Emily Kelley, Research Associate; Robert Will, Cartographic Assistant

Copyright The Newberry Library 2003

Early History

County development did not begin in California until after the area came under the control of the United States. Beginning in the mid 1700s, California was explored and colonized by Spain, but Mexico's independence from Spain in 1821 resulted in California falling under the authority of Mexico. Settlement was primarily limited to a narrow area along the Pacific coast, while knowledge of the interior remained sketchy. During the years of Mexican rule, from 1822 to 1848, Mexico created ranchos, missions, ayuntamientos, and districts, often with overlapping jurisdictions, to extend civil and religious authority over the settled parts of California. However, unlike Texas, where the early Mexican municipalities became the first counties, there is no direct linkage between the Mexican civil jurisdictions and the original California counties.

One feature of the Mexican period did have an important influence on the development of county lines—the Mexican land grants, or ranchos. Eight hundred thirteen land grants were made under Mexican rule, and many of them figure in county boundary descriptions from the earliest days to the present. While the use of land grant boundaries suggests a precision in the delineating of county lines, the reality was often quite different. Rancho boundaries were often vaguely defined, and most land grants were not actually surveyed until long after their incorporation in county boundary descriptions. For this project, the surveyed lines of land grants are used in mapping boundaries, unless other evidence demonstrates that another line was in actual use.

California Statehood

Unlike almost all other western states, California never achieved territorial status. From 1846, when United States troops first landed in California during the Mexican War, until September 1849 when delegates met to draft a new state constitution, authority was fragmented among remnants of Mexican civil bureaucracy, U.S. military rule, and various extralegal endeavors such as the Bear Flag Revolt. The constitutional convention met in September 1849 in Monterey, decided to skip the territorial phase, and proceeded directly to craft a state constitution. Matters then moved quickly, and the state government went into operation on 20 December 1849 when Peter Burnett was inaugurated first governor of California. The state legislature also began meeting in December, although the United States Congress did not officially admit California to the Union until 9 September 1850.

County creation was one of the most important issues facing the new legislature, and in February 1850 it passed an act creating twenty-seven counties that covered all of the state's territory. Thus, except for Mare Island, California had no "non-county" areas that existed outside the bounds of a county, a phenomenon that was common to many other states. However, this desire to establish at least some semblance of government oversight in every corner of the state did not translate into neat, clear, unambiguous county boundary lines. Early legislators recognized their lack of geographical knowledge of the interior, and many of these early interior boundaries were defined in the most general terms. For example, the northern boundary of Calaveras County was first described in 1850 as "following the summit of the dividing ridge between Moquelumne and Cosumne rivers; thence due east to the State boundary line" (California Laws 1849, 1st sess., ch. 15, sec. 25/p. 63). There was also a question of whether mining districts should be incorporated into counties, given their transitory populations. Despite some opposition in the legislature, the districts were included in the final county creation bill that was passed on 18 February 1850.

In 1852 California became involved in the first of two county disputes with Nevada. California proposed Pautah County to be located entirely in present Nevada (then Utah Territory), contingent upon the United States transferring a large portion of Utah Territory, including Pautah, to California. That never occurred, and in 1859 California abandoned efforts to organize Pautah County.

The second dispute was less calculated and due more to lack of information. The boundary between California and Nevada began to be surveyed in the 1860s, although the official surveys were not completed until 1873. In 1861, Mono County was created along the eastern border of California. No one actually knew precisely where the state line was, and Aurora became the county seat of Mono County. About the same time Nevada territorial officials made Aurora the county seat of Esmeralda County, Nevada Territory. Thus Aurora had the distinction of simultaneously serving as the county seat of two counties located in different states. In the fall of 1863, the boundary commission reached Aurora and determined that it lay about three and one-half miles inside Nevada, thus ending its tenure as county seat of Mono County, California.

The creation of California counties proceeded rapidly, from the twenty-seven original counties created in 1850 to the creation of California's fifty-eighth county, Imperial, in 1907. Since that time, no major changes have taken place in county boundaries, although numerous smaller adjustments have occurred. As the federal land survey proceeded through California, many of the boundary changes shifted county lines from less precise features, such as ridge lines or lines run due east or west from a certain point, to boundaries running on the federal land survey lines. Most California counties became fully organized immediately after their creation. This is in contrast to other states where counties often remained unorganized for years, or even decades. Only four of the original California counties were unorganized and attached to fully organized counties: Colusa, Marin, and Trinity for periods of fifteen months or less; Mendocino for nine years.

Twentieth Century Changes in County Boundaries

In 1941, the state legislature passed an act that permitted the changing of county boundaries without going through the legislative process (California Laws 1941, 54th sess., ch. 493/pp. 1801–1805). The boards of supervisors of the affected counties were allowed to make changes, following strict requirements set forth in the law. For example, counties were not permitted to move a line more than five miles, or reduce the size of any county by more than five percent. Counties were required to file such changes with the Secretary of State and the State Board of Equalization. The original act of 1941 has been amended several times and is still in force. The State Board of Equalization provided a list of some two-dozen boundary changes filed since 1944. Individual counties were contacted to obtain copies of the relevant ordinances and resolutions; wherever possible, the changes have been mapped. In a few cases, detailed information could not be obtained. At the same time laws regarding county boundaries continued to be passed by the legislature. In some cases, these simply codified a change already decided between two counties; in other cases, the legislation appears to be unrelated to local decisions.

Small Changes and Proposed Counties

Very small changes (indicated by “_pt.shp”) are not mapped on the California Interactive Map of Historical Counties. However, information on these changes is provided in the chronologies, which include the date of change, counties involved, and the source of the information. The locations of most small changes in California are available as part of the California Tiny Changes shapefile. (For information about the GIS files see the Atlas of Historical County Boundaries homepage).

Counties whose creations were authorized by the legislature, but never took effect, are known as “proposed” counties. Information on proposed counties is provided in the chronologies. Proposed counties can be viewed on the interactive map by activating the “Unsuccessful Proposals” Layer. Proposed changes between existing counties are not available on the interactive map, but they can be found in the California Historical Counties shapefile (see the homepage for more information).


California is one of a handful of states for which a well-done county boundary compilation exists. Owen C. Coy's, California County Boundaries (1923, reprinted 1973), was very useful for this project. This carefully researched work provides a lot of background information on the "Why" of county formation and includes information on discussions that took place in legislative committees, much of which did not result in actual boundary legislation. The Mexican Land Grant maps in Warren A. Beck and Ynez D. Haase's, Historical Atlas of California (1974) were helpful for correctly locating ranchos mentioned in boundary legislation.

Historical maps do not frequently play a large role in these compilations and are treated as secondary, rather than primary sources. Still, historical maps occasionally are indispensable for identifying lost landmarks and names of individual landowners. Important historical maps for California included the forty-two county landownership maps from the Library of Congress reproduced on microfiche. Also useful were Topographical Railroad and County Map of the States of California and Nevada, A. C. Frey and Co. (1868); William M. Eddy's 1854 Official Map of the State of California; and Britton and Rey's Map of the State of California, compiled by George H. Goddard (1857). These three can be viewed online at the David Rumsey Map Collection,


Special thanks are due David J. Martin of the California State Board of Equalization for researching and supplying a list of boundary changes reported to that office since 1944. Queries to several dozen counties were met with generous responses. County board members, county administrators, LAFCO officials, and clerks of the boards of supervisors took time to track down county ordinances and minutes of board meetings. This work would not be as comprehensive without their assistance.