One of the clearest trends in American religion is the increased number of people who do not affiliate with a religion. Lots has been said about it, mostly trying to figure out if it's real (it is), and why it's happening.
Sometimes overlooked in this discussion is who are the religiously unaffiliated.
It turns out that perhaps a majority of the non-affiliated actually have religious beliefs, they just don't affiliate with a religion. Depending on the data that you look at, about 1/2 have some belief in God. For example, 1/5th of them believe in God without any doubt, and another fifth believe with only occasional doubts. (Data from Fischer and Hout, 2006, Century of Difference, p. 193).
As such, this group might best be described as the religiously unaffiliated rather than no-religion people, for they frequently have strong religious beliefs.
(Correspondingly, some people who affiliate with churches can be labeled as agnostic/ atheist).