A firefighter was hurt while battling the blaze.
Firefighters took a defensive position as it was upgraded to a 2-11 fire, with the blaze spreading to the Cricket Wireless store next door, police said.
The roof of the dollar store collapsed in the fire. The extent of damage to the cell phone store was unclear early Friday.
The fire has been extinguished.
One firefighter suffered minor injuries to his hand and was taken in stable condition to the University of Chicago Medical Center.
The cause of the fire is under investigation.