Ibelieve the passage below shows the origins of the brand of Unitarianism to which Eliot's family belonged. It evolved from one of the original nonconormist Churches in England, the Congregationalists, which came to the colonies to avoid persecution.
The Pilgrims sought to establish at Plymouth Colony a Christian fellowship like that which gathered around Jesus himself. Congregationalists include the Pilgrims of Plymouth, and the Puritans of the Massachusetts Bay Colony, which were organized in union by the Cambridge Platform in 1648. These settlers had John Cotton as their most influential leader, beginning in 1633. Cotton's writings persuaded the Calvinist theologian John Owen to separate from the Presbyterian church. He became very influential in the development of Congregationalist theology and ideas of church government. Jonathan Edwards, considered by some to be the most important theologian produced in the United States, was also a Congregationalist.
The history of Congregational churches in the United States is closely intertwined with that of American Presbyterianism, especially in New England where Congregationalist influence spilled over into Presbyterian churches farther west. Some of the first colleges and universities in America, including Harvard, Yale, Dartmouth, Williams, Bowdoin, Middlebury, and Amherst, all were founded by the Congregationalists, as were later Carleton, Grinnell, Oberlin, and Pomona.
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, and transcendentalism.
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. Prompted by a controversy over an appointment in the theology school at Harvard, in 1825 the Unitarian churches separated from Congregationalism. Most of the Unitarian "descendants" hold membership in the Unitarian Universalist Association, founded in the 1960s by a merger with the theologically similar Universalists. This group had dissented from Calvinist orthodoxy on the basis of their belief that all persons could find salvation (as opposed to the Calvinist idea of double predestination, excluding some from salvation.)