Untrue. His wife burned the letters he had, but there are still letters and stuff he wrote to others. Pretending that we have nothing, but still know his actions are that he prayed not to Christ and spoke of going to church for his wife's sake, is solely pretense. We get it from what he wrote.
We're not getting this from nowhere, some people tried to use the fact that he went to the Episcopalian church as evidence of his beliefs, he made it clear that they were not and continued to keep his true beliefs private. If such were not the case there would have been no need for people to question again his beliefs as he left office.
Personally it matters not what he believed to me, only that we have more evidence of Deism, including generic references to god such as calling him "Providence" than we do of Christianity. We know full well what Jefferson thought of Christ as a God, he removed such references in the New Testament he wrote and that still doesn't matter.
None of their beliefs would make us a "Christian" nation, even if they were Huckabee and preached of Christ daily before they held office. We are a nation with a secular government where most of the population happens to be Christian, but we are not a Christian nation.