The city of Simi Valley (from the Chumash word, Shimiyi), in the eponymous valley, is in the southeast corner of Ventura County, California, United States, 40 miles (64 km) from downtown Los Angeles, making it part of the Greater Los Angeles Area. The city sits next to Thousand Oaks, Moorpark, and Chatsworth. The city's 2019 population has been estimated at 125,613, up from 124,243 in 2010. The city of Simi Valley is surrounded by the Santa Susana Mountain range and the Simi Hills, west of the San Fernando Valley, and northeast of the Conejo Valley. It grew as a commuter 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. The Reagan Library has hosted Republican primary debates, the last in 2012, and the first primary debate in 2016.
Simi Valley was once inhabited by the Chumash people, who also settled much of the region from the Salinas Valley to the Santa Monica Mountains, with their presence dating back 10,000–12,000 years. Around 5,000 years ago these tribes began processing acorns, and harvesting local marshland plants. Roughly 2,000 years later, as hunting and fishing techniques improved, the population increased significantly. Shortly after this sharp increase a precious stone money system arose, increasing the viability of the region by offsetting fluctuations in available resources relating to climate changes.