Police spokesman Anthony Guglielmi said a female sergeant was on her routine patrol near the intersection of Cermak and Western when she heard a loud sound and the windshield of her squad car shattered.
Police initially believed that shots had been fired at the officer. They later said someone threw a rock at the car, and shots were not fired. Police said no bullet casings were found, but a rock was found on the windshield.
The sergeant was hit by flying glass and taken to the UI Health to be looked over as a precaution.
An investigation into the incident is ongoing. The squad car was taken to the 10th District for evidence collection.