The shooting took place just after midnight along Belmont Avenue and River Road in River Grove, River Grove Police Chief Michael Konwinski said.
Police determined unknown occupants of a vehicle fired a weapon at the bus, which was stopped at the intersection.
The bus driver then took the vehicle to Franklin Park to find a safe location and parked it in the 3300-block of North River Road.
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The four people injured were taken to Loyola University Medical Center and Gottlieb Memorial Hospital, Franklin Park fire Acting Deputy Chief Lt. Daniel Fidonik said. He did not provide any information about their conditions, but one person later died, police said.
Police blocked off part of North River Road, as they worked to determine preliminary information later Saturday morning. What appeared to be a party bus could still be seen in the area about 6:30 a.m.
M&M Limousine Services in Des Plaines owns the bus. A spokesman for the company said the driver is OK but would not provide any additional details on the incident.
The West Suburban Major Crimes Task Force is assisting in the investigation.