The attack took place at the Bellingham Retirement Community in West Chester at around 6.30pm.
The scene has been shut off as police continue to search for Bruce Rogal, 59, who is suspected of killing his parents at the retirement facility, before fleeing the scene.
He is also suspected of attempting to kill his ex-wife earlier on Wednesday evening.
Investigators believe Mr Rogal is driving a 2002 silver Hyundai Odyssey, with Pennsylvania number plates ENN3549, and is considered armed and dangerous.
Mr Rogal’s divorce was finalised on Tuesday, with his home being awarded to his ex-wife, according to reports.
He is believed to have driven to his ex-wife’s home in West Bradford Township on Wednesday evening, before shooting at her while she changed the oil in her car.
His ex-wife was not hurt, but nearby homes sustained damage from the shots.
Mr Rogal then proceeded to his parents’ retirement home in East Goshen Township, where he shot and killed them, according to police.
Police have implemented a two-mile radius lockdown surrounding the retirement community following the shooting.
West Chester Area School District also issued an alert, stating they had locked down schools in the area.
Chester County District Attorney Tom Hogan said the search for Mr Rogal continue in Chester County, nearby counties and neighbouring states.
Mike Galczyk, whose daughter works in the retirement home, expressed his fear over the attack.
He said: “She’s texting us saying she’s hiding inside with her team.
“She told us to stay safe out here.”
“She said ‘We’re on lockdown.’ At first I thought she was kidding.”
The Bureau of Alcohol, Tobacco, Firearms and Explosives reported they were responding to the incident.
They said: “ATF is responding to a shooting at a retirement home in West Chester, Pennsylvania.”