San Diego is a county located in Southern California.
San Diego . It is in San Diego County , on the coast of the Pacific Ocean in Southern California , approximately 120 mi south of Los Angeles and immediately adjacent to the border with Mexico . Southern California . The region is traditionally described as eight counties , based on demographics and economic ties : Imperial , Los Angeles , Orange , Riverside , San Bernardino , San Diego , Santa Barbara , and Ventura . The Los Angeles area has over 12 million inhabitants , while the Riverside-San Bernardino area has over 4 million inhabitants and the San Diego area has over 3 million inhabitants .