Congregationalism originated from the English Puritan movement of the 16th century. Some radical Puritans broke away from the Church of England to become Separatists and found independent congregations.
Separatists believed that church membership was reserved exclusively for convinced believers in Jesus Christ, and that God had given each congregation the authority to determine who might participate in its sacraments and join in its rites and ministries. The Pilgrims who came to America in 1620 were Separatists.
By the end of the 17th century in America, the Puritans in Massachusetts Bay Colony had effectively created a separate Protestant denomination, the Congregationalist Church. Congregationalism remained the dominant religious force in New England until the middle of the 19th century. It was the established, state-supported church in Connecticut until 1818 and in Massachusetts until 1833.
In the period 1800-1840, many Congregationalist churches in the Boston area became Unitarian churches.
In 1957 the Congregational Christian Churches united with the Evangelical and Reformed Church to become the United Church of Christ. Other Congregationalist denominations include the National Association of Congregational Christian Churches (NACCC) and the Conservative Congregational Christian Conference (CCCCUSA). They are considered to be more conservative than the UCC, but only in comparison to the very liberal United Church of Christ. Both of these smaller church federations allow their affiliated congregations a wide latitude in doctrinal matters and, of course, more local autonomy than is typical of Protestant denominations.