The fire happened around 2:30 a.m. on Saturday in a three-flat apartment building at 78th and Phillips, Chicago police said.
A 24-year-old man died in the fire, while four people were rescued, including the boy.
The boy, identified as 7-year-old Adrian Matias Peña, died while in the hospital, the medical examiner said.
A 2-year-old boy was also rescued from the fire, his condition was not disclosed.
A 24-year-old woman was taken to University of Chicago hospital in good condition and a 27-year-old man was taken to Trinity Hospital for non-fire related injury, police said.
At least 23 people were displaced by the fire.
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The cause of the fire remains under investigation.