San Diego County, officially the County of San Diego, is located in the southwest corner of the U.S. state of California, north to its border with Mexico. As of the 2020 census, the population was 3,298,634; it is the second-most populous county in California and the fifth-most populous in the United States. Its county seat is San Diego, the second-most populous city in California and the eighth-most populous in the U.S. It is the southwesternmost county in the 48 contiguous U.S., and is a border county. It is home to 18 Indian reservations, the most of any county in the U.S. There are 16 military installations of the U.S. Navy, Marine Corps, and Coast Guard in the county. Collected from Wikipedia.