Police said someone found the child wandering alone in an alley near the 1800 block of South Spaulding Avenue around 4 a.m.
The boy was only wearing a diaper and a T-shirt, police said.
The child was taken to Mt. Sinai Hospital and appears to be in good condition.
Police said the child was safely reuinited with his family around 6 a.m.
It was not immediately clear why the boy was outside alone.
The Department of Children and Family Services is investigating.