The facility was built between 1886 and 1910, and the doors were opened to its first 150 young offenders in September 1896. After housing over 155,000 men in its lifetime, the doors to the prison closed December 31, 1990.
Most of the grounds and support buildings, including the outer wall, have been demolished since the closing. In 1995, the Mansfield Reformatory Preservation Society was formed. They have turned the prison into a museum and conduct tours to help fund grounds rehabilitation projects and currently work to stabilize the buildings against further deterioration.
If it looks familiar, it most likely is due to it being featured in the movie Shawshank Redemption. It also appeared in several other movies, such as Air Force One (some movie artifacts remain), music videos (Godsmack's "Awake", Lil Wayne's "Go DJ"), and probably every ghost hunting tv show ever created.
For more information on the site and tours visit their official website: http://www.mrps.org/