Adams was raised a Congregationalist, but ultimately rejected many fundamental doctrines of conventional Christianity, such as the Trinity and the divinity of Jesus, becoming a Unitarian.

Paine was a Congregationalist and a devout Christian. He worked as a full-time Congregationalist clergyman, among other occupations, prior to signing the Declaration of Independence. Later he left Congregationalism and Calvinism and embraced Unitarianism, which during that era was an alternative denomination within Protestant Christianity. Paine was a firm believer in the divine origin of the Christian religion. He gave full credence to the scriptures, as a revelation from God, designed to instruct mankind in a knowledge of their duty, and to guide them in the way to eternal happiness.

President Thomas Jefferson was a Protestant. Jefferson was raised as an Episcopalian (Anglican). He was also influenced by English Deists and has often been identified by historians as a Deist. He held many beliefs in common with Unitarians of the time period, and sometimes wrote that he thought the whole country would become Unitarian.

The legitimate powers of government extend to such acts only as are injurious to others. But it does me no injury to my neighbor to say there are twenty gods or no god. It neither picks my pocket nor breaks my leg

In general, most Franklin scholars have found him to be quite moderate in his attitude toward religion. Typically, Alfred Owen Aldridge has described Franklin as a confirmed Deist, who, in contrast to more militant Deists like Tom Paine, did not attempt to "wither Christianity by ridicule or bludgeon it to death by argument."

Without higher courts to ensure doctrinal uniformity among the congregations, Congregationalists have been more diverse than other Reformed churches. Despite the efforts of Calvinists to maintain the dominance of their system, some Congregational churches, especially in the older settlements of New England, gradually developed leanings toward Arminianism, Unitarianism, Deism. By the 1750s, several Congregational preachers were teaching the possibility of universal salvation, an issue that caused considerable conflict among its adherents on the one side and hard-line Calvinists and sympathizers of the First Great Awakening on the other. In another strain of change, the first church in the United States with an openly Unitarian theology, the belief in the single personality of God, was established in Boston, Massachusetts in 1785 (in a former Anglican parish.) By 1800, all but one Congregational church in Boston had Unitarian preachers teaching the strict unity of God, the subordinate nature of Christ, and salvation by character. Harvard University, founded by Congregationalists, became a center of Unitarian training.