The cause has been deemed accidental, CFD said.
Milan Campbell was killed in the fire on Valentine's Day in the 2700-block of Granville Avenue in West Rogers Park.
READ MORE | Child dies, mother, 2 Chicago firefighters injured in West Rogers Park apartment building fire: CFD
The boy's mother was hospitalized in critical condition. Her condition Wednesday was not immediately clear.
Two firefighters were also taken to a hospital in good condition, after stairs on which they were standing collapsed, CFD said.
Firefighters said the fire started in the first-floor unit, where the mother and child lived.
The boy was badly burned, and his mother tried to rescue him, CFD said.