Eric Zielinski and Heather Sturwold, both 18, were identified as the victims, the coroner's office said.
Zielinski was driving the vehicle when it left the roadway and hit a tree near the intersection of Briggs Street and Spencer Road in Joliet.
Zielinski was pronounced dead at 4:35 a.m.
Sturwold was a passenger in the vehicle and taken to Silver Cross Hospital in New Lenox, where she was pronounced dead at about 5 a.m., according to the coroner's office.
Joliet police are investigating.