The fact is that the percentage of people identifying as Protestant has declined since the 1970s while the total number of Protestants has increased (62 percent of Americans identified as Protestant in 1972 and only 51 percent did so in 2010). Yet because of the population increase in the U.S., there were 28 million more Protestants in 2010 than in 1972.

So did Protestantism in America decline since the 1970s? Yes (percentwise) and no (total numbers).
What about when we drill down to the denominations that comprise Protestantism in America? Here the differences depend on whether we look at short-term or long-term trends.

If we look at the short-term (year-to-year) trends, we may be able to detect a decline in some groups, especially in large denominations. For instance, the membership of the Southern Baptist Convention--the largest Protestant denomination in America--declined by 105,708 from 2011 to 2012. While that sounds like a lot of people, the denomination could lose that many members every year for 150 years before the pews in SBC churches would be completely empty.

In the case of the SBC, and other conservative denominations, the trend seems to be that they're losing members to other conservative denominations, especially non-denominational ones. As of 2010, four percent of Americans (12,200,000) worshipped in a nondenominational church. There are almost as many members of nondenominational churches as there are members of the SBC--and almost as many as in all of the mainline churches combined. A decline in a conservative denominational church is often offset by an increase in a conservative non-denominational church.

When tracking changes to gauge the overall health of a denomination, it makes more sense to look at long-term trends. If we look back 50 years (to 1965) we can see a clear and unequivocal trendline: liberal denominations have declined sharply while conservative denominations have increased or remained the same.

Here are the primary mainline denominations, every one of which has seen long-term decline in membership:

Christian Church (Disciples of Christ)
In 1965, the CC(DoC) had 1,918,471 members. In 2012, the membership was 625,252, a decline of 67 percent.

United Church of Christ (Congregationalist)
In 1965, the UCC had 2,070,413 members. In 2012, there were 998,906 members, a decline of 52 percent.

The Episcopal Church
In 1966, the TEC had 3,647,297 members. By 2013, the membership was 1,866,758, a decline of 49 percent.
(Those numbers should be even lower, though, since those figures by the TEC include breakaway churches trying to leave the denomination.)

Presbyterian Church (U.S.A.) (PCUSA)
In 1967, the PC(USA) had 3,304,321 members. In 2013, the membership was 1,760,200, a decline of 47 percent.

Reformed Church in America
In 1967, the RCA had 384,751 members. In 2014, the membership was 245,217, a decline of 36 percent.

United Methodist Church (UMC)
In 1967, the UMC had 11,026,976 members. In 2012, the membership was 7,391,911, a decline of 33 percent.

Evangelical Lutheran Church in America (ELCA)
In 1987, the ECLA had 5,288,230 members. In 2013, the membership was 3,863,133, a decline of 27 percent.
(Note: The ELCA was formally constituted in 1988 as a merger of the Lutheran Church in America, the Association of Evangelical Lutheran Churches and the American Lutheran Church.)

American Baptist Churches
In 1967, the ABC/USA had 1,335,342 members. In 2012, the membership was 1,308,054, a decline of 2 percent.

(Note: The ABC/USA has been able to stem its decline among white congregants by replacing them with African American and Hispanic members.)
Now let's look at a few of the primary non-mainline denominations, almost every one of which has increased in membership since the mid-1960s.

Church of God in Christ
In 1965, the CoG had 425,000 members. In 2012, the membership was 5,499,875, an increase of 1,194 percent.

Presbyterian Church in America
In 1973, the PCA had 41,232 members. In 2013, the membership was 367,033, an increase of 790 percent.
(Note: The Presbyterian Church in America was founded in 1974 by conservative members of the Presbyterian Church in the United States who rejected that church's merger with the United Presbyterian Church in the U.S.A.)

Evangelical Free Church of America
In 1965, the EFCA had 43,851 members. In 2013, the membership was 372,321 , an increase of 749 percent.

Assemblies of God
In 1965, the AoG had 572,123 members. In 2013, the membership was 3,030,944, an increase of 430 percent.

African Methodist Episcopal Church
In 1951, the AME had 1,166,301 members. In 2012, the membership was 2,500,000, an increase of 114 percent.

Southern Baptist Convention
In 1965, the SBC had 10,770,573 members. In 2013, the membership was 15,735,640, an increase of 46 percent.

Lutheran Church-Missouri Synod
In 1965, the LCMS had 2,692,889 members. In 2012, the membership was 2,163,698, a decline of 20 percent

Mainliners may try to comfort themselves by claiming that every denomination is in decline, but it's simply not true. While conservative churches aren't growing as quickly as they once were, mainline churches are on a path toward extinction. The mainline churches are finding that as they move further away from Biblical Christianity, the closer they get to their inevitable demise.

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