As of the United States 2000 Census, FSP and SAC had a combined inmate population of 7,246 housed at level 1 and 2 security, the two lowest levels of security for prisons operated by the CDC. Level 1 prisoners are housed in open dormitories without a secure perimeter, and Level 2 prisoners may be housed in open dormitories with secure perimeter fences and armed guard coverage. However, there are no dormitories within the FSP secure perimeter, and prisoners are housed in one man cells, two to a cell. In 2004, the majority of level 2 prisoners were moved to other prisons and level 3 prisoners took their place. FSP's population in early 2005 was approximately 3,400.
There are five housing units within the secure perimeter, including the original two-tiered structure. Unit 1 is the most populous cellblock in the United States, with a capacity of nearly 1,200 inmates on four five-tiered sections.
All cells include toilet, sink, bunks, and storage space for inmate possessions. There are two dining halls, a large central prison exercise yard, and two smaller exercise yards. The visiting room includes an attached patio as well as space for non-contact visits.
FSP is California's second-oldest prison, long known for its harsh conditions in the decades following the California Gold Rush. Construction of the facility began in 1878 on the site of the Stony Bar mining camp along the American River. The prison officially opened in 1880. Inmates spent most of their time in the dark behind solid boiler plate doors in stone cells measuring 4 feet by 8 feet (1.2 by 2.4 m) with 6 inch (150 mm) eye slots. Air holes were drilled into the cell doors in the 1940s, and the cell doors are still in use today.
FSP was the first prison in the world to have electric power, which was provided by the first hydroelectric powerhouse in California. The quarry at FSP provided granite for the foundation of the state capitol and much of the gravel used in the early construction of California's roads.
Although FSP now houses primarily medium security prisoners, FSP was one of America's first maximum-security prisons; a total of 93 prisoners were hanged at FSP between December 13, 1895, and December 3, 1937. After that time executions were carried out in the gas chamber at California's San Quentin Prison.
The Folsom Prison Museum is located on the prison grounds, which is open to the public from 10 a.m. to 4 p.m. There was also a shop with inmate-made handicrafts for sale to the public, but it closed in 2005.
FSP has been the location of a number of feature films, including Riot in Cell Block 11, Heat, American Me, The Jericho Mile, Another 48 Hours, Diggstown, parts of Walk the Line (a biopic of Johnny Cash), and Inside the Walls of Folsom Prison, which was the inspiration for Cash's song. The television drama 21 Jump Street also featured FSP when Johnny Depp's character Tom Hanson was imprisoned for murder. And a few shots for the movie Pros and Cons. The prison was central to the documentary film, "Code of Silence" by Amy Happ FSP was renamed for the movie "Frankie and Johnny" with Al Pacino. In the FSP Museum there is the identification of the fake Penitentiary.