The voters of 1800 were citizens of a nation generally of white Christians. The unchurched made up almost90% of that group, meaning they had no official membership in a congregation.
"John Quincy Adams was associated with
Unitarianism, though he had strong Christian beliefs and frequently read the Bible in its original Hebrew and Greek. While he explored Unitarianism, he ultimately rejected its denial of Christ’s divinity, affirming his belief that Jesus was God incarnate."
www.christianity.com
"Thomas Jefferson’s religious beliefs were complex and unconventional. He was most comfortable with
Deism,
theistic rationalism, and
Unitarianism. While he admired Jesus' moral teachings, he rejected Christ’s divinity, biblical miracles, and the concept of the Trinity. Jefferson even created his own version of the Bible, known as
The Jefferson Bible, which excluded supernatural elements and focused solely on Jesus' ethical teachings.
Despite his personal beliefs, Jefferson was a strong advocate for religious freedom and the separation of church and state. He famously coined the phrase
"a wall of separation between Church & State" in a letter to the Danbury Baptists in 1802." Encyclopediavirginia.org
Let me add that Jefferson was Anglican then Episcopalian in membership, for to hold office in Virginia one had to be a vestry member.