San Diego is a city in the U.S. state of California located alongside the Pacific Ocean in Southern California. With a population of over 1.3 million residents, the city is the eighth-most populous in the United States and the second-most populous in California after Los Angeles. The city is located immediately adjacent to the Mexico–United States border and is the seat of San Diego County, which has a population of nearly 3.3 million people as of 2021.