The child's identity has not been released.
Chicago firefighters were told a child was trapped upon their arrival at the three-story, courtyard building on Wednesday afternoon. The child's body was found during a search in the third-floor unit.
Officials said the fire appears to have been contained to that one unit. Two other people were able to get out on their own. They were transported to St. Francis Hospital in Evanston, and their injuries are not known.
Officials have not said what caused the fire.