The officer was driving near 179th Street and LaGrange Road when they were involved in a crash with another car, Tinley Park police said.
Both drivers were transported to a local hospital, police said. The off-duty officer was later pronounced dead. Their identity was not immediately known.
The Chicago Police Department also confirmed the driver who died was an off-duty officer from the department.
The other driver's condition was not immediately known.
No further information about the crash was immediately available.
Tinley Park police are investigating.