The United States is on the verge of becoming a minority Protestant country; the number of Americans who report that they are members of Protestant denominations now stands at 51%. Moreover, the Protestant population is characterized by significant internal diversity and fragmentation, encompassing hundreds of different denominations loosely grouped around three fairly distinct religious traditions — evangelical Protestant churches (26.3% of the overall adult population), mainline Protestant churches (18.1%) and historically black Protestant churches (6.9%). While Americans who are unaffiliated with any particular religion have seen the greatest growth in numbers as a result of changes in affiliation, Catholicism has experienced the greatest net losses as a result of affiliation changes. While nearly one-in-three Americans (31%) were raised in the Catholic faith, today fewer than one-in-four (24%) describe themselves as Catholic.
Source: Pew Research Center