Axel Cruz, 4, died from injuries sustained in the fire Wednesday, the Cook County Medical Examiner's Office said.
The other three children who died in the fire were identified to the medical examiner's office as Aiden Cruz, 5; Jayden Cruz, 6; and Angel Rodriguez, 11.
The video in this story is from a previous report
The deadly blaze was in the West Humboldt Park neighborhood's 4000-block of West Potomac Avenue Sunday morning, police said.
Two adults were also injured in the blaze, police said. A 40-year-old woman was taken to West Suburban Hospital in good condition with minor smoke inhalation, officials said. A man, 35, was taken to St. Mary's with minor smoke inhalation and was in good condition, police said.
Flames blocked the back door the only exit - forcing the mother to break a window and escape, Chicago Fire Department spokesman Larry Langford said.
Investigators determined the fire was caused by an open flame in one of the back rooms, Langford said.
Sun-Times Media Wire contributed to this report