About 100 people were expected to take part in the seven-day march organized by the National Association for the Advancement of Colored People (NAACP), with more joining segments of the long walk, NAACP staff member Jamiah Adams told Reuters.
The march, reminiscent of the civil rights marches of the 1960's, was set to begin at midday on Saturday (local time) at the Canfield Green Apartments, the residential complex near where 18-year-old Michael Brown was shot and killed on Aug. 9 by Ferguson police Officer Darren Wilson.
A grand jury's decision on Monday not to charge Wilson ignited protests in Ferguson and a riot that left buildings torched and stores looted.
Demonstrations spread to major cities across the United States, resulting in hundreds of arrests during the week.
Protests in Ferguson had dwindled in size and intensity in the days after the grand jury decision, then gained renewed energy on Friday as demonstrators temporarily shut down a St. Louis-area mall and turned up in force at other shopping areas across the country.
In Ferguson, there were at least 16 arrests overnight, police said, and dozens of others in other cities.
The NAACP expects about 1,000 people to be part of the final leg of the "Journey for Justice" march, said Adams, who will participate in the march along with other NAACP staff members and the organisation's president, Cornell William Brooks.
"We are resolute and excited to get started and moving forward in something that's positive, a nonviolent demonstration toward criminal justice reform and police reform," Adams said.
The civil rights group is asking participants to protect themselves against icy conditions expected along the route by wearing hand warmers and wool socks.
The NAACP is also calling for a new police chief in Ferguson and a national law to prevent racial profiling by police.
Marchers will be able to shuttle back and forth between the walk and their residences in the St. Louis area, by taking a bus back to a staging area, Adams said.
