By the early twentieth century, American Congregationalism had grown comfortable enough with cooperation to begin merging with bodies that had never shared its exact New England origins. In 1931 the National Council of Congregational Churches united with the Christian Connection, a smaller, non-creedal movement with roots on the early American frontier, to form the Congregational Christian Churches. That body, in turn, entered the much larger 1957 union that produced the United Church of Christ, joining with the Evangelical and Reformed Church to create a denomination whose government blended congregational independence with a more connectional structure.
Not every Congregationalist church agreed to go along. A minority judged the 1957 merger too great a departure from local church autonomy and the tradition's historic reluctance to bind itself to any wider ecclesiastical body, and declined to enter the United Church of Christ at all. Some had already organized the National Association of Congregational Christian Churches in 1955, in anticipation of the merger, explicitly to continue congregational polity outside it; others had formed the Conservative Congregational Christian Conference in 1948 for related, more theologically conservative reasons. Both bodies continue today as small, independent fellowships of self-governing churches.
The tradition's deepest legacy may still be the one it set in 1853, when the First Congregational Church of South Butler, New York, ordained Antoinette Brown, the first woman ordained to the ministry by a mainstream American denomination, a landmark local churches could reach entirely on their own authority, without waiting for any wider body's permission.