Actually the unitarianism thing probably isn't correct. I looked it up after I posted and the source had changed its info. I've noticed people who wish to portray our nation as originally irreligious use a lot of BS info, like portraying George Washington as a deist. Deists don't get baptized : ) I even wonder about the purposes of the Jefferson Bible. Jefferson appears to have been a Godly man. But about Newton, he said "I have a fundamental belief in the Bible as the Word of God, written by those who were inspired. I study the Bible daily." A unitarian wouldn't believe the Bible is the inspired Word of God; they deny too much of it.
Isaac Newton attempted to secretly publish essays attacking the concept of the Trinity. He was afraid to publish them in england. (I wonder why.)
That's the Unitarians. Newton's beliefs were personal and were unitarian in nature. That is, he firmly rejected the doctrine of the Trinity, based on his historical study of the Arian heresy.
Cf. Westfall, The Life of Isaac Newton, under Arianism in the index. "The mere thought of trinitarianism, the 'fals infernal religion,' was enough to fan Newton into a rage." And Newton blamed it for what he saw as the degraded practice of Christianity, represented chiefly by Roman Catholicism, but not excepting Anglicanism.
Newton came near to sacrificing his academic career for his beliefs, as he was prepared to refuse ordination into the Anglican Church, which had been a requirement for his position at Cambridge, and would have involved swearing to beliefs abhorrent to him. Fortunately, we may say, some adroit politicing voided this requirement in the nick of time.