San Diego County is a county of the United States that is located in the southwestern corner of the State of California. Hence, San Diego County is also located in the southwestern corner of the 48 contiguous United States. Both the county seat and largest city of San Diego County is the city of San Diego. The population of San Diego County was about 2,813,835 in the 2000 U.S. Census. In July 2008, an estimate by the U.S. Census Bureau set its population at about 3,001,000 people, making San Diego County the third-most-populous county in California, just behind its northern neighbors Orange County and Los Angeles County.