MAINLINE PROTESTANT: Congregationalist

We ask you, brothers, to respect those who labor among you and are over you in the Lord and admonish you, and to esteem them very highly in love because of their work. 

1 Thessalonians 5:12,13 ESV

Congregational means that the Congregation runs itself. They don't like higher Church authority. Any higher Church structure usually only sets general policy or is administrative. The congregations usually do as they please.

There were two main movements of Congregationalism as the main focus of the Church.

One came out of the Anglican Church in England initially as "independent Churches". Many were banished to America and would later form denominations in a Congregational format (the Pilgrims were of this group). Many of these were divided between Calvinistic Predestination and Arminian Free Will -- but strongly rejected Once-saved-Always-saved. Today most are Amillennial.

The second came out of a Lutheran background in Scandinavia and merged together in America as the Evangelical Free Church as they drew in many Methodists and Presbyterians at the time and moved from Luther to Evangelicalism. They further moved into Evangelical circles in recent years due to the image and influence of their top radio minister Chuck Swindoll.

--The United Church of Christ is the biggest of these Congregational Churches due to forming from a merger of the Congregational Church with some of the Conservative Congregational Churches and the Evangelical and Reformed Church. Over the years they drew in many nondenominational Black Theology congregations too. What was left of the Congregations of the Congregational Church simply changed to a new name of National Association of Congregational Christian Churches. Two conservative splinter groups have left the United Church of Christ forming the The Evangelical & Congregational Reformed Church as well as the Midwest Congregational  Fellowship that is more Calvinistic. Many leaders of the United Church of Christ, atlough officially more Arminian Free Will, dabble in Universalism or Pluralism.

As a sidenote the Evangelical Church (liberal) had merged with the German Reformed Church (conservative) a couple of decades before to from the Evangelical & Reformed Church which later merged with the Congregationalists to from the United Church of Christ. Many who joined the two split offs from the United Church of Christ had come from the German Reformed Church side. 

As for that previous merger that had formed the Evangelical & Reformed Church what was left of the German Reformed Church who didn't want to join with the Evangelical Church at the time became the Reformed Church in the United States.

1) From the Anglican background:

National Association of Congregational Christian Churches (Liberal)

Conservative Congregational Church (Moderate-Conservative)

United Church of Christ (Ultra-Liberal)

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***Evangelical & Congregational Reformed Church (Conservative)

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*** Midwest Congregational  Fellowship (Conservative)

2) From the Lutheran Background:

Evangelical Free Church (Conservative)