Illinois State Police say the boy was ejected from the SUV in the one-car crash. He was taken to Comer Children's Hospital where he was pronounced dead.
Officers say the 46-year-old male driver and the SUV were found near the top of the 83rd Street ramp. The driver was also taken to the hospital.
Police say the car was also carrying a 23-year-old woman, 1- and 2-year-old boys, and a 3-month-old girl.
Police say the driver of the 2001 Ford Expedition lost control of the vehicle. The Ford then veered from the middle right lane to the far right lane and onto the right shoulder, state police say. Authorities say the Ford then struck the guardrail on the right shoulder twice. As the Ford struck the guardrail, the 4-year-old boy was ejected from the back passenger window, police said.