ISP said troopers responded to the crash on southbound I-55 near Weber, in Romeoville, around 12:40 a.m.
The pedestrian involved in the crash was transported to a local hospital, where they were pronounced dead, ISP said. Their identity was not immediately released.
ISP said another crash, which involved three vehicles, followed that collision. No injuries were reported in the second crash.
What caused the crashes was not immediately clear.
All southbound lanes were temporarily closed, and lanes reopened just after 5 a.m.
Authorities are investigating. Further information was not immediately available.