Arlington Heights Fire Chief Lance Harris said firefighters responded at about 11:52 p.m. to the complex at 2315 E. Olive St.
"When they opened the door to the east wing, they were hit with heavy smoke," Chief Harris said.
Firefighters found heavy smoke in one unit where the man was found on a couch. He was transported to a hospital with life-threatening injuries, Chief Harris said.
Residents in 48 units in the complex have been displaced. The fire has displaced 48 residents of the complex.