European settlement in what is now San Diego County began with the founding of the Mission San Diego de Alcala by the Spanish, in 1769.
San Diego County became part of the United States as a result of the Treaty of Guadalupe Hidalgo in 1848, ending the U.S.-Mexican War. This treaty designated the new border as terminating at a point on the Pacific Ocean coast which would result in the border passing one Spanish league south of the southernmost portion of San Diego Bay, thus ensuring that the United States received this excellent natural harbor.
San Diego County was one of the original counties of California, and was created at the time of statehood in 1850. It was named after San Diego Bay, which had been rechristened in 1602 by Sebastián Vizcaíno in honor of the Franciscan St. Didacus of Alcalá, known in Spanish as San Diego de Alcalá de Henares, and whose name was borne by Vizcaíno's flagship.
As originally created in 1850 San Diego County was quite large and included most of southeastern California south and east of Los Angeles County. As such it included major parts of what are now Inyo, San Bernardino, Riverside, and Imperial counties.
The later part of the 19th century witnessed numerous realignments of county boundaries. The most recent changes were the creation of Riverside County, in 1893, and Imperial County, in 1907.
According to the U.S. Census Bureau, the county has a total area of 4,526 sq mi (11,721 km²). 4,200 sq mi (10,878 km²) of it is land and 326 sq mi (843 km²) of it (7.20%) is water.
San Diego County has varied topography. On its western side is seventy miles of coastline. Snow-capped mountains rise to the northeast, with the Sonoran Desert to the far east. Cleveland National Forest is spread across the central portion of the county, while Anza-Borrego Desert State Park occupies most of the northeast.
North San Diego County is known locally as "North County"; the exact geographic definitions of "North County" vary, but it includes the northern suburbs and sometimes certain northern neighborhoods of the city of San Diego.
The eastern suburbs are collectively known as "East County", though most still lie in the western third of the county. The southern suburbs and southern detached portion of the City of San Diego, extending to the Mexican border, is collectively referred to as "South Bay".
Towns and Cities in San Diego County
Carlsbad
Chula Vista
Coronado
Del Mar
El Cajon
Encinitas
Escondido
Imperial Beach
La Mesa
Lemon Grove
National City
Oceanside
Poway
San Diego
San Marcos
Santee
Solana Beach
Vista
