Folsom is a city in Sacramento County, California, United States. The population was 80,454 at the 2020 census, up from 72,203 residents …Folsom is a city in Sacramento County, California, United States. The population was 80,454 at the 2020 census, up from 72,203 residents at the 2010 census. The Nisenan tribe of Native Americans had long inhabited the area. The Gold Rush of 1849 brought violence, disease and overwhelming loss for the tribes.