El Centro is a city in and the county seat of Imperial County, California, United States. El Centro is the most populous city in the Imperial Valley, the east anchor of the Southern California Border Region, and the core urban area and principal city of the El Centro metropolitan area which encompasses all of Imperial County. El Centro is also the most populous U.S. city to lie entirely below sea level. The city, located in southeastern California, is 113 miles (182 km) from San Diego and less than 20 miles (32 km) from the Mexican city of Mexicali.