The shootings took place just before 5:00 p.m. Tuesday on the 200 block of Spring Street.
All four victims were taken to Capital Health Regional Medical Center. Three were suffering from non-life-threatening injuries. The fourth victim remains in critical condition.
Investigators are trying to figure out if the quadruple shooting was a retaliation attack for a deadly shooting and chase that took place in the city on Monday.
Trenton police are investigating.