city and port of entry, Imperial county, southern California, U.S. It is located at the southern end of the Imperial Valley and is separated from the city of Mexicali, Mexico, by a reinforced steel fence. Founded in 1900, Calexico was once a tent town for the Imperial Land Company. It developed as a trade and shipping centre and a port of entry, with some light manufacturing, but transnational tourism is the economic mainstay. Near the city limits is the All-American Canal, which irrigates the valley. The city's name, like that of Mexicali, is a combination of the names California and Mexico. Inc. 1908. Pop. (1990) 18,633; (2000) 27,109.