It happened Sunday around 3:30 a.m. at 1105 Sansom St.
Firefighters went into the building and found three-year-old Sanranadee Green Libby in her bedroom.
She was taken to St. Mary's Hospital where she died in the emergency room.
Streator Police and Fire Departments are investigating the fire, along with the LaSalle County State's Attorney and the Illinois State Police Crime Scene Services.
WMBD 31 reported last week the city is offering a reward to try and solve an arson problem. A number of fires have started lately.
Authorities have not confirmed if Libby's death is the result of a fire that was started intentionally.