The boy was on the roller coaster ride called Python Pit with his twin brother at the Go Bananas amusement park Saturday evening when he managed to get under the ride's safety bar, the Chicago Tribune reported Sunday.
The ride was in motion at the time of the accident and the boy fell to his death, although he apparently suffered head injuries before striking the ground, officials said.
The Chicago Sun-Times said there were no height requirements posted at the ride, but it was believed he met all requirements for the ride.
The unnamed boy was from Dolton.
It appears to be "just a tragic accident," said Norridge Police Chief James Jobe.
The park was closed while a state inspector performed a preliminary investigation.
No one answered the phone at Go Bananas early Sunday.