The crash happened Thursday night on I-57 near 135th Street in Posen, officials said.
Illinois State Police say the trooper was standing next to a vehicle that had been pulled over. That's when they say another driver hit the trooper's squad car and the pulled-over vehicle, which then pushed the trooper backwards into a ditch.
The driver was arrested and charged with aggravated DUI, police said.
No further information was immediately available.
ISP continues to investigate.