representative pete stark (D. - Calif), is the first openly non-theistic member of congress, as reported by the secular coalition for america. there are most likely other nontheists in congress.... if you assume that the US congress represents the people of america and somewhere between 2 and 10% of americans are nontheists (atheists, freethinkers, humanists, and agnostics).
'Although the Constitution prohibits religious tests for public office, the Coalition's research reveals that Rep. Stark is the first open nontheist in the history of the Congress. Recent polls show that Americans without a god-belief are, as a group, more distrusted than any other minority in America. Surveys show that the majority of Americans would not vote for an atheist for president even if he or she were the most qualified for the office.
Herb Silverman, president of the Secular Coalition for America, attributes these attitudes to the demonization of people who don't believe in God. "The truth is," says Silverman, "the vast majority of us follow the Golden Rule and are as likely to be good citizens, just like Rep. Stark with over 30 years of exemplary public service. The only way to counter the prejudice against nontheists is for more people to publicly identify as nontheists. Rep. Stark shows remarkable courage in being the first member of Congress to do so."'
(i thanked rep. stark for his courage here: http://www.house.gov/stark/contact/index.htm.)