It is not known what connection those people, one man and three women, may have to the shooting. Their names have not been released.
The shooting happened behind an apartment complex in the 1500 block of Elmwood Street around 10 a.m. Friday.
Officer Christopher Dorman, 25, was dispatched to the location for a report of people smoking narcotics. Authorities say he was shot after confronting the suspects.
Sources say Dorman was hit in the face, torso, and lower extremities. He was wearing his protective vest at the time.
"I was told by the doctors that 'thank God he had his vest on,' so apparently there may have been several shots to his vest," Chief Robert Ruskowski said at a news conference.
One nearby resident told Action News he was standing near an open window when he heard three rapid gunshots. There was a short pause, followed by four rapid shots.
We talked to another resident who heard at least six gunshots.
Officer Dorman has been on the force for just over a year.
"Outstanding officer, I can't say enough about him," said Chief Ruskowski. "Outstanding."
Ruskowski said Dorman's mother and father are at the hospital, "obviously upset but relieved that he's stable."
He has undergone one surgery and was getting ready for a second, Ruskowski said.
Police activity focused on residential area adjacent to Folcroft rail station after officer shot multiple times. pic.twitter.com/3QEWwDxc5h— John Rawlins (@JRawlins6abc) June 24, 2016
Both SEPTA and Amtrak halted service through Folcroft for the investigation, but both have since resumed.