At about 6 p.m., the boy fell from the window from a home in the 7600 block of South Coles.
The boy apparently got up while mom was still sleeping and went near the window.
Police called the incident an accident. The boy was taken to Comer's Children's Hospital.
Neighbors said a man walking by saw the child on the ground in the gangway and got help.
Investigators spent two hours on scene talking with the mother and neighbors and walking through the gangway where the child was found.