Fire officials say seven of those 11 residents from the building at 6244 N. Winthrop were in serious condition.
Officials say at least one man jumped from a window, and others were forced to hang out of windows to escape the flames.
In addition to smoke inhalation, there were other, more serious physical injuries.
"One person jumped and that was in the rear in the courtyard," said John McNicholas, Chicago Fire Department.
"I went to the window and saw several people at their windows, some of them trying to climb out so I did the same ' cause it was the only way I could go. Fortunately, there was a drain pipe there that I climbed down to the ground," said Glenn, tenant.
The blaze began in a third floor unit toward the back of the building. The occupant was able to get out and warn his neighbors.
"I opened the doors, there was black smoke, couldn't get out. I opened the windows, turned on the shower. I waited for instructions," said Zachary Warren.
"I heard someone screaming help, so we all ran outside and then on the top three windows there was people hanging out asking for help," Loyola student Stephanie Jarosd.
Most of the fire damage involved the third and fourth floors of the building. But water damage has also affected units on the first and second floors and the basement units.
One Loyola student, who had a basement apartment, isn't sure what to do next.
"I called my mom and started crying because all my stuff is in that building, so I know for a fact since it started on the floor above me, the structure more than likely is going to collapse...so I was really freaking out about it," said Martin Gomez.
Forty people have been displaced.
The fire department hasn't given an exact cause of the fire except to say it was accidental.
The building is located next to a Loyola University building, which was also evacuated as a precaution.