Simi Valley ( ; Chumash: Shimiyi) is a city in the valley of the same name in the southeast region of Ventura County, California, United States. Simi Valley is 40 miles (65 km) from Downtown Los Angeles, making it part of the Greater Los Angeles Area. The city borders Thousand Oaks, Moorpark, and the Chatsworth neighborhood of Los Angeles. As of the 2020 U.S. Census the population was 126,356, up from 124,243 in 2010. The city of Simi Valley is surrounded by the Santa Susana Mountains and the Simi Hills, west of the San Fernando Valley, and northeast of the Conejo Valley. It grew as a bedroom community for the cities in the Los Angeles area and the San Fernando Valley when a freeway was built over the Santa Susana Pass. The Ronald Reagan Presidential Library, where the former president was buried in 2004, is in Simi Valley.