This is a weird one, because I've always seen people make out that all the Founding Fathers were Christian, when they were not, and that would be the Bad History post. Some people on reddit have gone the other way however, and act like none of them were Christian. (Some of the replies do call him out on it though.)

The post in question

That the founding fathers were Christian. Many, in fact, were deists, a popular religious movement at the time that suggested that the world was created by a god who didn't really care about what happened in the world, and therefore didn't intervene. Some, like Thomas Jefferson, were Christian deists, a sect of Christianity that embraced Christ's moral teachings but denied his divinity and thought that God didn't really want anything to do with our world. Google the Jeffersonian Bible.

I'm not sure by what way to measure who counts as a Founding Father here and who not, so it may change around a bit.

From what I can find, of the 55 delegates to the 1787 Constitutional Convention, 49 were Protestants, and two were Roman Catholics. Out of the Protestants, 28 were Anglican, eight were Presbyterians, seven were Congregationalists, two were Lutherans, two were Dutch Reformed, and two were Methodists. I'm not sure about the 4 other people, I'm assuming a mix of Deist, Unitarian or just unknown?

Also I will point out, the people talking about Unitarians as if the Unitarians of the 18th Century are the same as modern day Unitarian Universalists. While I'm sure some are the same, Unitarian Universalists are a very open, accomodating group, Unitarians then were a much more strongly Christian influenced faith, who rejected the Trinity.

While many of the most famous founders were Deist, Unitarian or in other ways hugely went against Orthodox Christianity, or just had private religious beliefs. Those that weren't Christian still were massively influenced by it, to quote Colonial Williamsburg historian Linda Rowe here said, “Franklin, Washington, and Jefferson all attended church services frequently to the end of their lives. They gave money to church building funds of several denominations, and attended Baptist, Presbyterian, Episcopalian, and Unitarian houses of worship. Most made no secret of their conviction that regular religious practice was necessary to public virtue upon which the survival of the republic depended.”

Anyway, with the major founding fathers, Jefferson and Franklin were most likely Deists, strongly influenced by Christianity, with Jefferson flirting with Unitarianism, being friends with Joseph Priestley and attending servives while in Philadelphia, Thomas Paine was definitly a Deist, Washington and John Adams, changed their religious views over time, with Washington being especially private about his views, and Adams was raised a Congregationalist but shared many views with Deists, while not necesarilly being one himself, saying about Thomas Paines' Age of Reason "The Christian religion is, above all the religions that ever prevailed or existed in ancient or modern times, the religion of wisdom, virtue, equity and humanity, let the Blackguard Paine say what he will.".

To say that the Founding Fathers were Christian or weren't Christian are both wrong. They are a large group of people (that still Historians can't agree who is included in that) with many different religious beliefs. Let me know if I made any mistakes in this, not exactly the area of history I know most about.