Metra said the crash happened in Oak Park. Union Pacific West Line Train #507 left Chicago at 240 p.m. and was heading to Elburn when it struck a trespasser near the platform.
That person has died, a Metra spokesperson confirmed.
That train is stopped as Metra police and law enforcement investigate.
The CTA said Green Line trains are experiencing significant delays due to police activity near North Harlem Avenue and Lake Street.
Bus shuttles are available from Harlem and Lake to Laramie and Lake, the CTA said.