They carried hand-painted posters with slogans decrying Obama's proposed health care reforms, or accusing the Democratic administration of leading the United States down the road to socialism.
"With the bad economy, it can really affect some people, like the lifestyle of certain people. It's affecting us at home... not so we can't eat at night but that's why we have to get involved now -- so it doesn't get too bad," his 13-year-old sister Megan, who was holding her own sign, said.
The march, coordinated by Freedomworks, a grassroots movement calling for lower taxes, less government and more economic freedom for all Americans, drew demonstrators from across the United States.
Police at the Capitol were unable to say how many people had turned out for the rally, but at mid-afternoon, the crowd stretched out of sight from the legislature and onto the National Mall, sources said.