Crews were on the scene in the 5900-block of South Elizabeth Street in Chicago's Englewood neighborhood just before 1 p.m.
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CFD said the elderly person was taken to University of Chicago Medical Center Tuesday, initially in critical condition.
The victim was later identified as a 77-year-old man, Robert Wayne Davis, according to the Cook County Medical Examiner's Office.
The cause of the fire has been ruled an accident due to mishandling of smoking materials, fire officials said.
Video of the scene appeared to show the fire took place in a home, and a large number of police officers and firefighters responded.
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It was not immediately clear how the fire began.