The 21-year-old woman succumbed to her injuries in hospital on Saturday, according to police.
Two other people died Friday and another remains in critical conditions.
Fire crews were called to the apartment on 1068 Dovercourt Road near Dupont Street just after 3:10 a.m. Friday. The building has a second-floor, four-bedroom apartment above a vacant store.
A man was found badly burned near the door of the apartment unit and was pronounced dead at the scene. Three other victims, a man and two women, were also found in the apartment.
All of the victims were rushed to hospital, without vital signs, where one woman died Friday afternoon.
According to fire officials all the victims were young adults.
The fire is believed to have started in the living room, but the matter is still under investigation.