Robert J. Turner, 32, died in the intensive care unit at University of Illinois Medical Center Friday after being transferred there from the Dixon Correctional Center Wednesday, the Chicago Tribune reported.
At the jail, Turner was being treated for a number of illnesses, including cirrhosis of the liver, authorities said.
The Cook County medical examiner's office determined Turner died of necrotizing fasciitis, or the flesh-eating bacteria, and sepsis.
The flesh-eating disorder is a rare infection that can destroy the muscles, skin and other underlying tissue.
Turner was serving a 40-year sentence the shooting death of Derek Miles, 18, in 1998. Chicago police said Turner, then 18, and two other men killed Miles in a home invasion.