The fire consumed the entire unit, and the cause was not known Sunday evening.
There are reports that the unit's owner was overheard saying she had somehow caused it. Neighbors tried to get her out, but it was ultimately an off-duty fire fight who may have saved her life.
Emergency personnel responded to the fire on the 21st floor of the building. Firefighters arrived on the scene within three minutes of the call, but already residents were pouring out of the building, including two who lived on the floor where the fire broke out.
"I shut the door, and I just ran. I got onto the 22nd floor and got on my cell waiting for the elevator, I called my mom and started screaming and yelling," resident Christine Dzurovsak.
"I saw this woman standing there on the phone. I said, "What happened?" She said, 'I did it.' She was so scared and stunned she just stood there. I said, 'Let's go', but she wouldn't move," said Mona Sutaria, also a resident.
Off-duty firefighter Jason Durbin was riding past the building in a private ambulance when he saw flames. He ran into the building and up 28 flights of stairs.
"She was about five or six feet in there. She was still conscious but knocked out from the smoke. I grabbed her, drug her out to the hallway, caught my breath, and took her down," Durbin told ABC7 Chicago.
Durbin has been a firefighter 15 months, and even though he was off-duty, he said there was no question in his mind it was the right thing to do.
"Anybody in our profession would do the exact same thing. There was no reason to stand down there and just watch," he said.
The unit's owner was taken in serious condition to Northwestern Memorial Hospital. She is said to have been suffering from smoke inhalation but has not yet been identified.
It was not clear Sunday night whether or not some residents of the building would have to relocate.