In his book,
Christians Are Hate-Filled Hypocrites ..., Dr. Bradley Wright used Steensland *, et al's (2000) RELTRAD classification system, which identifies seven groupings to describe the religious bodies in the United States. The designations "include, but are not limited to" the religious bodies/persuasions listed below.
Evangelical Protestants: the Southern Baptist Convention; some Independent Baptists; many non-denominational Protestant churches; the Lutheran Church; Missouri Synod; the Presbyterian Church in America; the Assemblies of God; the Church of Christ; the Church of the Nazarene; the Free Methodist Church; and the Seventh-day Adventist Church. They tend to be theologically and socially conservative.
Mainline Protestants: the American Baptist Church in the USA; the United Methodist Church; the Evangelical Lutheran Church in America; the Presbyterian Church, USA; the Episcopal Church in the USA; and the United Church of Christ. They tend to be theologically and socially liberal or "progressive".
Black Protestants: the National Baptist Convention; the African Methodist Episcopal Church; the Church of God in Christ. All of these denominations are primarily, but not exclusively, African-American. They tend to be conservative in theology but more liberal in social views.
Catholics: Roman Catholics. Although the Orthodox would probably object to being listed with the Catholics, I believe that they would be included in this group in this classification system.
Jewish: Separated into Orthodox, Conservative, and Reform traditions. The Orthodox represent historic Judaism, the Reform are more liberal and modern, and the Conservatives are in the middle.
Other Religions: Islam, Buddhism, Hinduism, Jainism, Sikhism, Mormonism, Jehovah's Witnesses, Christian Science, Oneness Pentecostals, and Unitarian-Universalism. Some of these groups self identify as Christian but are rejected as heterodox by other Christians.
Religiously Unaffiliated: Atheists, Agnostics, and "Don't Cares."
* Steensland, Brian, et.al., "the Measure of American Religion: Toward Improving the State of the Art,"
Social Forces, 79(1), 2000, pp. 291-318.