The attack took place just before 9 p.m., police said, and the man fled down Kimbark on foot.
The victim, a 47-year-old woman, said the offender told her not to scream. She received minor injuries on her elbows.
The victim got off the train at the Metra stop in Riverside around 8 p.m. on Tuesday night. She told police she believes her attacker then followed her before the assault, which took place in an alley across the street from the station. The victim was not sure whether the suspect was on the train with her or if he followed her from the platform. Several neighbors heard screams, but most thought it was just kids playing.
Riverside residents are concerned.
"It's very shocking. It hasn't settled in yet," said Erin Furlough, resident.
In a news release, Riverside Chief Tom Weitzel said, "Officers are following up on several leads including canvassing the area where incident was reported to have taken place, re-interviewing the victim, making arrangements for a composite sketch and searching the Metra train station and trains for video surveillance recordings."
The victim was only able to give police a general description of her attacker.
In the meantime, security has been stepped up at Longcommon crossing.