Oceanside is a city on the South Coast of California, located in San Diego County. The city had a population of 174,068 at the 2020 United States census, up from 167,086 at the 2010 census. The city is a popular tourist destination, owing to its historic landmarks, beaches, and architecture. Oceanside's origins date to 1798, when the Spanish founded the village of San Luis Rey with the establishment of Mission San Luis Rey de Francia by Fermín de Lasuén.