A Cook County Jail inmate found unconscious in his cell Tuesday afternoon was pronounced dead at a hospital, police say.

Correctional staff found Michael O’Connor unresponsive in his cell in the Residential Treatment Unit of the lockup, 2700 S. California Ave., about 4:25 p.m., the Cook County Sheriff’s Office said.

Security and medical staff began life-saving measures until paramedics arrived and transported O’Connor, 33, to Mount Sinai Hospital, police said. He was pronounced dead a short time later.

O’Connor was being held in lieu of a $100,000 D-bond on felony charges of aggravated intimidation of a peace officer, intimidation/physical harm, threatening a public official and harassment/obscene proposal/threat to kill for allegedly repeatedly sending threatening and obscene messages to a Chicago police officer.

While in custody, O’Connor was also charged with two counts of aggravated battery to correctional staff.