Ariel Castro was found hanging in his cell just after 9:00 pm Tuesday night.
Jail workers performed CPR on Castro and he was quickly taken to a local hospital but was pronounced dead just before 11:00 pm.
When he first arrived at the jail Castro had been on suicide watch and was under constant observation.
But after showing no signs of problems for several weeks those watches were removed.
Still, his cell was in a protective custody area and was checked every 30 minutes.
Castro was serving a life term in prison for kidnapping three women and repeatedly raping them in his home for nearly a decade.
Castro's attorneys had tried without success to have a psychological examination of their client Castro done before he was turned over to state authorities.
They said Castro clearly fit the profile of sociopathic disorder and they hoped researchers would study him for clues that could be used to stop other predators.
Castro was sentenced to life in prison plus 1,000 years on his guilty plea to 937 counts including kidnapping and rape.