The Cook County Medical Examiner's Office declared Neriyah Beller dead Monday evening, the Chicago Tribune reported.
Police said they suspected the girl's father, Nathaniel Beller, doused his family with a flammable liquid and set the fire early Saturday.
Also killed in the house fire was the children's mother, Taniya Johnson, officials said.
The 29-year-old Beller was declared dead Sunday, officials said.
The couple's son, Naciere Beller, was in "very critical" condition Monday night at an area hospital with burns over 35 percent of his body, the Chicago Sun-Times reported. The girl sustained burns to 100 percent of her body, the hospital said.