San Diego is a city in Duval and Jim Wells counties, Texas, United States. The population was 3,748 at the 2020 census and 4,488 at the 2010 census. It is located primarily in Duval County, of which it is the county seat.

Duval County is a county located in the U.S. state of Texas. As of the 2020 census, its population was 9,831. The county seat is San Diego. The county was founded in 1858 and later organized in 1876. It is named for Burr H. Duval, a soldier in the Texas Revolution who died in the Goliad Massacre.