Rancho Cucamonga, CA. Online Offers. Rancho Cucamonga is a suburban city in San Bernardino County, California, United States. As of the 2010 census, the city had a population of 165,269, up from 127,743 at the 2000 census. L. Dennis Michael was elected as Mayor on November 2, 2010. Jack Lam is the City Manager. The city was incorporated in 1977, as a result of a vote among the residents of the unincorporated communities of Alta Loma, Cucamonga, and Etiwanda. Money's Best Places to Live 2006 ranked Rancho Cucamonga as #42 in America.