San Francisco incorporated as a city

Background. San Francisco became part of the United States in 1848 via the Treaty of Guadalupe Hidalgo. The California Gold Rush starting in 1848 caused a massive population boom, increasing residents from 1,000 to 25,000 by December 1849. This rapid growth transformed the settlement into a major commercial and financial center in the American West.

Incorporation. California was admitted to the Union on September 9, 1850. The State of California subsequently chartered San Francisco and San Francisco County. San Francisco was established as one of the state's 18 original counties, serving as the county seat. At chartering, the city and county were not coterminous; the county then included territory that later became northern San Mateo County. Consolidation into a single city-county occurred in 1856.