Neighbors say the little girl chased after the basketball around 4 p.m. on 175th Street in Tinley Park.
Police say a 16-year-old boy was driving the car that hit the young girl. There's no immediate information on whether he'll face charges or citations.
The girl was identified by the Cook County Medical Examiner's office as 4-year-old Annabella Loerop.
Annabella, of the 6500-block of 175th St. in Tinley Park, where the incident occurred, was pronounced dead at Advocate South Suburban Hospital in Hazel Crest at 5:03 p.m., according to the medical examiner's office. An autopsy is scheduled for later Tuesday.
A basketball sat on the front lawn of the girl's house as distraught family members hugged one another on the front porch.
The car was eastbound on 175th Street when the girl was struck. Two postal workers driving westbound on 175th Street were on the scene seconds after the accident.
"It looked bad, very bad," Dee Diamond, of Matteson, said.
"I thought of my daughter when I saw the girl (lying) in the street," said Regina Mayerhofer, of Griffith, Ind., who called 911. "The girl has blue eyes and blond hair, just like my daughter."
Moments later, Diamond and Mayerhofer clasped their hands over their mouths and wept when Bettenhausen told them the girl had died.
"Oh, no. Oh, Lord. Oh, poor baby. Poor baby. She was so little, Lord have mercy to be with that family," Diamond said.
The Sun-Times Media Wire contributed to this report.