The shooting happened Tuesday afternoon in the North Kenwood neighborhood on the city's South Side.
15-year-old Hadiya Pendleton was shot in the back. She was transported in critical condition to Comer Children's Hospital, where she later died.
Police said Pendleton, who was a student at King College Prep, was not the intended target. She had reportedly performed with the school's band at President Obama's inauguration recently.
"An altercation started and some innocent people got shot," said community activist Andrew Holmes.
Police say a group of almost a dozen teenagers were under a canopy at a park in order to escape the rain. Another teen jumped the fence, approached the group and opened fire- hitting Pendleton.
A 17-year-old boy was shot in the leg. He is at Mercy Hospital.
The gunman then got into a car and drove away, according to police.
There is no information on a motive, and police are searching for a suspect.
Residents say the park is located in a quiet secluded block where neighbors look out for each other.
"It's innocent kids at the park, and somebody does something like that? It doesnt' make any sense," said Joe Thomas, resident.