Imperial County is a county located on the southeast border of the U.S. state of California. As of the 2020 census, the population was 179,702, making it the least populous county in Southern California. The county seat and largest city is El Centro. Imperial is the most recent California county to be established, as it was created in 1907 out of the eastern half of San Diego County. Imperial County is located in the far southeast of California, in the Imperial Valley.