It happened outside the UNO Pizzeria in the 1500 block of Providence Street, near Widener University, around 11 p.m. on Wednesday.
Sources tell Action News that three shooters opened fire on a crowd of about 30 people who were celebrating high school graduations.
A 19-year-old girl was shot in the shoulder, an 18-year-old boy was shot in the hip and a 17-year-old boy was shot in the leg, the sources say.
All three were taken to the hospital with non-life-threatening injuries. One has since been released, sources said.
Soures said there were upwards of 30 to 40 shots fired in the south parking lot.
A couple marked patrol units were also sitting across the street when it kicked off, sources added.
One graduated high school senior says his cousin was one of the victims.
"You just hear shots. Everybody just start scattering. Next thing you know, bullets flying right across your face. It was a life-or-death moment," said Eric, who was there when shots rang out.
Eric says he drove away as quickly as he could.
Chopper 6 was over the scene where there was a large police presence.
Investigators gathered evidence throughout the parking lot while also searching just beyond it with flashlights in a grassy area.
"I felt like a NASCAR driver, just speeding trying to get away. Hopefully nothing happens to either one of us because at the end of the day, it's not just my life in my hands, I got somebody else life too. And then everybody out here, just try to make sure everybody get to safety," he said.
Toni Alexander's daughter was at the party when the shots rang out. She came back to the scene Thursday morning to get her daughter's shoes.
"These are young adults these are 17-19 kids celebrating. They can't go nowhere around here without someone shooting," Alexander said.
Widener University released a statement following the incident saying they are "aware of the incident Wednesday night outside the Pizzeria Uno on Providence Avenue in Chester. City police are investigating and the university is fully cooperating with the department."
The circumstances surrounding the incident remain under investigation.