Gunfire erupted at around 8.25pm on Sunday at Gate City in Georgia Road, Birmingham, according to a report by news website AL.com.
Police said up to 60 shots were fired, likely from multiple guns.
Birmingham police spokesman Sergeant Bryan Shelton said all of the victims were innocent bystanders.
The five people who suffered gunshot wounds – but survived – are not believed to be in a critical condition.
The shootings took place around an hour after the protest ended in the community’s Lewis Park.
Many residents remained outdoors after the event.
“When the shooting started happening, people started dispersing,” said Sgt Shelton.
Residents described the chaos that ensued as the bullets rang out.
Xavier Story was tidying up after his son’s 1st birthday party. He told the news website: “I ran and tried to grab all the kids and get them inside.”
The 23-year-old saw the victim, who later died, collapse. “He had a pulse and we were fanning him and telling him, ‘they’re coming, they’re coming’,” he said.
Another resident described the shooting as “the scariest thing ever in my life”.
A mother-of-four, who had earlier attended the anti-violence rally, said: “It was peaceful like it was supposed to be.
“Everybody had a good time. I never would have thought that this would happen.”
Police are investigating the shooting, which took place near to where a police chase ended in a suspect being shot and wounded by an officer three days earlier.
News Source SkyNews