Firefighters were dispatched at about 9:51 p.m. near the Western Avenue grade crossing, police said.
The train conductor had found the teen near the Union Pacific-West railway tracks east of Western Avenue.
The 18-year-old died at the scene. His identify has not been released.
Police said foul play is not suspected.
Metra UP-W said their services were disrupted on Monday morning due to the investigation.
No other information was available.