Police spokeswoman Amy Dotson told Heart of Illinois ABC that about 200 people were gathered in the area at the time when shots rang out.
Dotson told WCBU that of the 12 people shot, 2 are in serious condition, with both individuals sustaining gunshot wounds to the neck.
None of the injuries are considered to be life-threatening, WCBU reported.
Two of the victims were transported to an area hospital in ambulances, while 10 were taken in private vehicles, according to the Journal Star.
There was no information regarding suspects released by officials. The incident remains under investigation.
The shooting added to an already violent weekend in Peoria, where one person was killed and three others were injured.
Hours before the riverfront shooting, police said a man was shot in the face just before 9 p.m. on Saturday just south of downtown Peoria.
On Saturday, police said a 40-year-old man was killed when he and another man were shot around 1:30 a.m. southwest of the downtown area.
Three hours later, officials responded to a ShotSpotter alert to find a vehicle that crashed into a home. The driver of the vehicle fled on foot, according to police.
Authorities later found out a man with a gunshot wound was dropped off at an area hospital. He is listed in serious condition.
Police said they believe that the occupants of two vehicles were shooting at each other when one crashed into a porch. The other vehicle fled.
Anyone with information regarding either of those incidents is asked to contact Peoria Police at (309) 673-4521 or CrimeStoppers anonymously at (309) 673-9000.