Camarillo is a city in Ventura County, California, United States. As of the 2020 United States census, the population was 70,741, an increase of 5,540 from the 65,201 counted in the 2010 Census. Camarillo is named for brothers Juan Camarillo, Jr. and Adolfo Camarillo, prominent Californios who owned Rancho Calleguas and founded the city. California State University Channel Islands, is housed on the former grounds of the Camarillo State Mental Hospital.