The fire started on a back porch and eventually spread to four houses.
At least three out of the four homes appear to be a total loss, and about 50 residents now have to search for someplace else to live.
Fortunately, though, no one was seriously hurt in the fire, the Fire Departement crediting the quick actions of a 12-year-old boy.
A cell phone camera captured the fire, which spread quickly from house to house.
"I looked out, and then the building next door was just in, it was just up, and the next thing you know all the buildings are going as well," said Jose Villarreal.
It happened shortly after 10 Saturday morning in the 4400 block of South Union in the Canaryville neighborhood.
Officials say the fire started on a back porch of one of the homes before quickly spreading to three others.
"These are all stick-built, framed, very close together, built a long time ago. So once they get going, they tend to take off," said Assistant Deputy Fire Commissioner Mark Nielsen.
Twelve-year-old Edwin Perez says he was in his kitchen when he saw smoke and flame and immediately warned residents in his multi-family house.
"My sister didn't want to wake up, so I just grabbed her, like, from the bed. I just grabbed her really hard and said, 'Wake up!'" Perez said.
With the fire spreading quickly, Perez says he then ran to his neighbors' homes.
"I was screaming, 'People, wake up! There's a fire in here!' And they all came out," he said.
"All's I heard was 'fire, fire, fire!' And the next thing you know, which direction to run, I didn't know. So I started going through the back, and that's when I see my bathroom on fire," Villareal said.
"I just seen the one little kid running out. Obviously he saved them," said witness Michelle Secor. "I mean, he did a great job."
No one was seriously injured in the fire and officials say Perez may have alerted as many as 50 residents in the four homes.
At the scene, the 7th grader was personally thanked by Chicago Fire Commissioner Jose Santiago.
"They're saying I was a great hero, and I did a good job up there," Perez said.
"That's an amazing young man," said Nielson. Twelve years old. He should be commended and praised."
The 12-year-old Chicago Public School student is crediting his quick action to the fire safety instruction that he received at his school, Alexander Graham Bell Elementary.
The cause of the fire is still under investigation.