The Will County Coroner's Office said the boy died at St. Joseph Medical Center Monday.
Another 17-year-old boy was previously charged with aggravated battery causing great bodily harm, police said.
He was processed at the Joliet Police Department and taken to the River Valley Justice Center.
The teen who died was found at the Riverwalk Homes Apartments at 366 N. Broadway St. just before 1 p.m. Sunday.
Officers recovered a knife from the scene.
Joliet police are investigating and asked anyone with information to call them at 815-724-3020. Anyone wishing to remain anonymous can contact Will County Crime Stoppers at 800-323-6734 or submit a tip online at crimestoppersofwillcounty.org.