San Diego (Spanish for Saint Didacus) is one of the 58 counties in the state of California. It was created in 1850, making it one of the original counties of the state. As of the 2010 census, the population was 3,095,313, up from 2,813,833 in 2000. The county seat and largest city is San Diego.
The county has 4,525.52 square miles (11,721.0 km2) of area, of which 4,199.89 square miles (10,877.7 km2) is dry land. San Diego is bordered by the Pacific Ocean on the west, Orange County on the northwest, Riverside County on the north and Imperial County on the east. To the south, the county borders Municipio de Tecate and Municipio de Tijuana, both in Baja California.