ISP said it happened in Posen around 1:40 a.m.
The trooper was investigating a crash on the I47th Street ramp to Interstate 57 northbound, parked with their emergency lights activated, ISP said.
ISP said that's when a vehicle rear-ended the trooper's squad car.
The trooper, who was inside the squad car at the time of the collision, and the driver involved were both taken to a local hospital with injuries.
Their conditions were not immediately known.
The investigation is active, and ISP did not immediately provide further information.