Most Protestants, 56 percent, expressed confidence in the church; a minority, or 46 percent, of Catholics did.
But Lydia Saad, Gallup senior editor, pointed out that the question deals with churches and organized religion. Americans generally remain a religious people, although increasingly on their own terms.
In 2007, a poll by the Pew Forum on Religion & Public Life found about one in six respondents said religion was "not too" or "not at all" important in their lives.
Five percent said they did not believe in God or a universal spirit.
Saad said "the church or organized religion" in 1975 was the highest-rated of the 16 institutions Gallup asked about.
Now it ranks fourth. The top three institutions Americans have most confidence in are, in order, the military, small business and the police.
The least-trusted institution is Congress, in which 13 percent of Americans voice "a great deal" or "quite a lot" of confidence.
Health maintenance organizations and banks follow right behind Congress.
The survey included 1,004 adults and was taken June 7-10.