Seattle police trailed the crowd, which zig-zagged through the downtown core without permission or a permit, leaving Sunday drivers stuck until the masses passed.
They said taking to the streets was one way to support Trayvon Martin and believe the system already failed his family.
"Justice was not served," said Charvell Price. "All the evidence points to the fact that he was murdered."
The Seattle rally began early in the day at Westlake Park. Many in the crowd believed Martin was executed and the jury's verdict is symbolic of the lingering racism in America that represses the poor and minorities.
"Trayvon Martin was killed because of his color, and because of what he wore," said Valerie Brooks.
Daman Hester, who is black, added: "I know if I had been on trial and it had been a little white boy, and I killed a little white boy, I would have been locked up, probably had to plead to 50 years."
Some in the crowd tempered their anger, saying there were complicated legal issues at play in what Zimmerman's lawyers presented as a self-defense case. They say the message they are sending today is just the start.
"Making noise always makes a difference," said Zawdie Terry. "Letting your voice be heard always makes a difference."
Although there were some masked participants in the crowd with a few holding clubs and bats, we are not aware of any reports of violence from this essentially peaceful demonstration.