San Jacinto is a city in Riverside County, California, United States. It is at the north end of the San Jacinto Valley, with Hemet to its south and Beaumont to its north. The mountains associated with the valley are the San Jacinto Mountains. The population was 53,898 at the 2020 census. The city was founded in 1870 and incorporated on April 20, 1888, making it one of the oldest cities in Riverside County.