Rancho Cucamonga (rănˈchō kōˌkəmängˈgə) [key], city (1990 pop. 101,409), San Bernardino co., S Calif. Situated in a vast suburban corridor, it is part of San Bernardino's metropolitan area. A rapidly growing residential area, it almost doubled in population between 1980 and 1990. Its varied manufacuturing produces metal and plastic products, processed foods, resin, metal coatings, and hardware. The city is the site of the restored 19th-cent. Casa de Rancho Cucamonga.