Stevenson Ranch is an unincorporated community in the Santa Clarita Valley of Los Angeles County, California. Stevenson Ranch is set in the foothills of the Santa Susana Mountains and lies west of Interstate 5 and the city of Santa Clarita. Stevenson Ranch encompasses about 6.4 square miles (17 km2). About 1,000 acres (4.0 km2) are set aside as parks, recreation areas, and open space. A master-planned community, it was approved by the county Board of Supervisors in 1985. The population was 20,178 at the time of the 2020 census. For statistical purposes, the Census Bureau has designated it a census-designated place (CDP).