Three people were transported from the scene at 79th and Halsted in fair condition; a fourth person is in good condition.
The city-owned building is more than 100 years old. City officials have declared it unsafe.
The building has stood empty for 20 years but Tuesday at 12:30 p.m., the 1880 structure began to crumble, sending pedestrians running.
"It started from the beginning of the building, it was like the domino effect. It started falling and the rest of it just came down with it," said DaJuan Watson, witness.
"That thing fall, so I just ran across the street by the bank and watched it fall, because I thought it was a car wreck," said Cleo Reed, witness.
Falling debris injured two people on the street and two others partially caught under scaffolding.
"So firefighters went in, lifted it up and pulled them out and got them to EMS right away," said Commissioner Robert Hoff, Chicago Fire Department.
Heavy equipment was brought in to search for a possible fifth victim buried under the rubble, but no one was found.
The fire department says the building just gave way after years of neglect.
"When you see a tree growing through the roof of the building that means the roof structure has deteriorated, and through the winters it has probably gotten frost and cold in there and it's eaten away at the mortar, and that's why it weakened the terra cotta on the front," said Hoff.
The fire commissioner says the building is extremely dangerous and must come down. It was once home to a Walgreens, but for the past 10 years the city of Chicago has owned the building.
"Over the years we tried to redevelop it or take it down. We have had several requests for proposals on the building. I believe it's an orange building, historical factor," said Ald. Latasha Thomas, 17th Ward.
A private company was on site to demolish the building Tuesday afternoon.