The collision happened about 5 p.m. at a railroad crossing in the 7700 block of West Grand Avenue, according to Chicago police and Metra spokeswoman Meg Reile.
The officer was taken to a hospital for treatment of unspecified injuries, but was expected to recover, according to a police spokesman. No other details were made available.
No injuries were reported for anyone on the train, which had about 100 passengers, Reile said.
The train’s engineer reported both the gate and warning lights were working at the crossing, Reile said.
Metra is investigating the incident.