It happened around 3:00 a.m. Sunday at the J & S Seafood Market on 9th and Kerlin streets.
Police say at least one gunman opened fire.
Three of the victims were found with gunshot wounds to the torso, including a woman in her 20s who was pronounced dead at the scene.
A fourth person - believed to be the shooter - was found with a self-inflicted gunshot wound to the head.
Two victims were taken to Crozier-Chester Medical Center while the alleged gunman was taken to the Hospital of the University of Pennsylvania. No word on their conditions.
Police say the corner where the shooting occurred is notorious for violence, with 59 calls in the past 10 years.
"We've had three murders, six robberies, several weapons assaults, 10 aggravated assaults, drug violations, four weapons violations, and a host of others," said Commissioner Joseph Bail of the Chester Police Department.
In a press conference Sunday morning Mayor John Linder said that J & S Seafood Restaurant has been closed until further notice by direction of the city and the health department.
