Aliso Viejo is a city in the San Joaquin Hills of southern Orange County, California. It had a population of 47,823 as of the 2010 census, up from 40,166 as of the 2000 census. It became Orange County's 34th city on July 1, 2001, the only city in Orange County to be incorporated since 2000. It is bordered by the cities of Laguna Beach on the west and southwest, Laguna Hills on the east, Laguna Niguel on the southeast, and Laguna Woods on the north.
The planned community of Aliso Viejo's original 6,600 acres were once part of the 26,000-acre Moulton Ranch, owned by the Moulton family, who took title in the 1890s to land originally granted to Juan Avila by the Mexican government in 1842. Over the years, portions of the ranch were sold and became Leisure World, Laguna Hills and Laguna Niguel. In 1976, the Mission Viejo Company purchased the remaining 6,600 acres to create a new planned community – Aliso Viejo – with a master plan for 20,000 homes for a planned population of 50,000. The master plan was approved by the Orange County in 1979, and homes were first offered for sale in March 1982. Aliso Viejo's first family moved in that November. As part of the project, 2,600 acres were dedicated to Orange County as part of the Aliso and Wood Canyons Wilderness Park, and 800 acres were set aside for local parks, recreation, schools and community facilities.