Lake Forest is a city in Orange County, California, United States. The population was 85,858 at the 2020 census. Lake Forest incorporated as a city on December 20, 1991. Prior to incorporation, the community had been known as El Toro. Following a vote in 2000, Lake Forest expanded its city limits to include the master-planned developments of Foothill Ranch and Portola Hills. This expansion brought new homes and commercial centers to the northeastern boundary of the city.