The Dodge Durango struck the CSX train about 2 a.m. at a crossing on the east side of Harvey, a south suburban community, killing the vehicle's four occupants, said Jason Baumann, a spokesman for the city of Harvey.
"It drove into the freight train," he said, adding that the crash remains under investigation.
Baumann said the bodies of the four people were removed from the SUV and would be identified by the coroner.
He said emergency crews in Phoenix, a Cook County village just east of Harvey, were alerted by a passerby that a vehicle was on fire. He said it wasn't clear if that person had witnessed the crash or had only seen the burning SUV following the impact.
Baumann said it wasn't immediately clear whether or where the train stopped after the collision, but when he arrived at the crash scene about 4 a.m. there was no train at the crossing and CSX workers were replacing crossing gates at the scene.
A message seeking comment from CSX was left Wednesday morning by The Associated Press.