Was trying to be mostly humorous about it, but there's good reason to think that a lot of the founding fathers were, if not athiest, then not-ardent-Christians. Some absolutely were devout christians. some were probably atheists. But it's bad politics- even today- to not be at least some form of christian.

that said originally, the amendment separating church and state was not inteded to protect the government from the church. it was intended to protect the church from the state. (I.E. many states had codified denominations with "others" being made... illegal.)