San Diego city is 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 . San Diego County is a county in the southwestern corner of the state of California , in the United States . Its county seat is San Diego , the eighth-most populous city in the United States . 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 .