The incident occurred shortly before 6 p.m. at the DoubleTree hotel, 5000 W. 127th St.
The girl was found unresponsive in the pool and taken to Advocate Christ Medical Center, where she died.
The girl was identified tot he Cook County Medical Examiner as 9-year-old Adriana Douglas of Highland Park, Mich. Witnesses said she was in the area participating in a cheerleading competition.
Foul play was not suspected in the drowning, police said.