Crowds of people waited for the announcement Monday night outside out of the county courthouse.
The grand jury looked at the case involving a white police officer who shot and killed a black teenager last August.
The death of Michael Brown, 18, triggered riots and looting.
A grand jury had considered the charges against officer Darren Wilson.
The National Guard was on hand to secure the county prosecutor’s office in anticipation of the announcement of the verdict.
Protestors planned to hold rallies across the nation, regardless of the grand jury’s decision.