WEBSan Diego County (/ ˌsæn diˈeɪɡoʊ / ⓘ), officially the County of San Diego (Spanish: Condado de San Diego), is a county in the southwestern corner of the U.S. state of California. As of the 2020 census, the population was 3,298,634, [7] making it California's second-most populous county and the fifth-most populous in the United States.