The Reason Rally, sponsored by 20 atheist, secular and humanist groups, was billed as the biggest-ever "coming-out" party.
An estimated 10,000 people rallied in Washington D.C. to celebrate the rejection of the idea of God.
The fastest growing 'religious' group is campaigning for a bigger place in public life.
Deep-seated fear of discrimination leads many Americans with no religious affiliation not to acknowledge themselves as atheists.
Thousands of atheists, agnostics and other non-believers turned out in the US capital on Saturday to celebrate their rejection of the idea of God and to claim a bigger place in public life.
The Reason Rally, sponsored by 20 atheist, secular and humanist groups, was billed as the biggest-ever "coming-out" party for the fastest-growing religious group in the United States -- those with no religion.
"There are too many people in this country who have been cowed into fear of coming out as atheists, secularists or agnostics," said the event's star turn, Richard Dawkins, the British scientist and best-selling atheist author.