The shooting happened inside the Lucky 7 store on the 1100 block of Morton Avenue around 11:20 a.m. Tuesday.
Police say officers arrived to find 27-year-old Dontae Dickerson on the floor of the store with a gunshot wound to the back of his head.
The shooting reportedly happened after an argument inside the store.
No arrests have been made.
Chester police ask anyone with information to contact City of Chester Police Department Detective Patrick Flynn (610) 447-8444 or Delaware County Criminal Investigation Division Christopher Karr (484) 745-5534.