Calabasas is a city in Los Angeles County, California, United States, located in the hills west of the San Fernando Valley and in the northwest Santa Monica Mountains between Woodland Hills, Agoura Hills, West Hills, Hidden Hills, and Malibu, California. As of the 2010 census, the city's population was 23,058, up from 20,033 at the 2000 census. The city was formally incorporated in 1991.The Leonis Adobe, an adobe structure in Old Town Calabasas, dates from 1844 and is one of the oldest surviving buildings in greater Los Angeles.