Timeline of Classical American Unitarianism:

I got that from this good historical resource site on Unitarianism. The secular left and religious right tend to fall into a false dichotomy of "Christianity" v. "Deism" as the political-theological drivers of the American Founding. Not enough attention is paid to this middle way theology, why I pay attention to it. It was most influential among the leading lights (i.e., the "key Founders") of the American Founding.

I reproduced from the above source until 1805.

1742 - Charles Chauncy writes Enthusiasm Described and Cautioned Against as a polemic against the Great Awakening..

1748 - Jonathan Mayhew delivers his Seven Sermons (published 1750), in which he argues that all have the right to make private judgments in religious matters and the duty to do so.

1750 - Ebenezer Gay assumes leadership of the Hingham Association, a group of ministers in southern Massachusetts who committed themselves to the fight for freedom from bondage to unreasonable doctrines.

1753 - Mayhew begins teaching the strict unity of God from the pulpit of the West Church in Boston.

1755 - Mayhew publishes 14 more sermons in his book, Sermons. He critiques the Calvinist views of predestination, justification by faith alone, and original sin.

1759 - Ebenezer Gay delivers the Dudleian Lecture at Harvard, Natural Religion as Distinguished from Revealed, wherein he argues that revelation can teach nothing contrary to natural religion or to the dictates of reason.

1784 - Charles Chauncy publishes treatise on universal salvation, The Mystery Hid From Ages and Generations.

1785 - King's Chapel in Boston, formerly Episcopalian, ordains Unitarian James Freeman, removes references to Trinity in prayer book.

1794 - English Unitarian Joseph Priestly arrives in America and helps establish churches in Philadelphia.

1805 - Unitarian Henry Ware is elected Hollis Professor of Divinity at Harvard.