The fire started at around 9:15 Wednesday morning at the Patrick Sullivan Apartments building in the 1600-block of West Madison.
Officials say that bedding on the ninth floor caught fire and quickly spread to the rest of the room. It triggered a full-building evacuation.
"The smoke was coming out from the eighth and ninth floor," Eddie Gates, evacuated resident, said. "One of the ladies from the ninth floor, I know they took her to the hospital."
The fire was put out just before 10 a.m.
Officials say the building-wide alert system was still being installed.
"People were calling the lobby to get advice. We made it clear to 911 that we were there for evacuation. If people call 911, the evacuation can be made clear," said Mark Nielson, assistant deputy fire commissioner.
The Patrick Sullivan Apartments were designated as senior housing in 2010 through the Chicago Housing Authority.