San Diego County, California was established on February 18, 1850 and named by Sebastian Vizcaino for Saint Didacus (Diego) of Alcalá, because the first Christian service in Alta California was held on the saint’s feast day, November 12th, 1602! Its county seat is San Diego, and its fair is held in Del Mar! You might recognize Cabrillo National Monument, the San Diego Zoo, Sea World, Mission San Diego de Alcalá, Anza-Borrego Desert State Park, and the Star of India, which are located in this county!