The most common reason for leaving church is a loss of faith, according to new research.
The number of Americans with no religion has increased from 16 per cent of the population to nearly a quarter in under a decade.
Growing numbers of adults, known as "nones', identify with no religious group, according to the latest study from Pew Research.
Nearly eight in ten of those with no religion rejected the faith of their childhood when they became adult.
For nearly half, this was due to a loss of faith.
One respondent said: "I'm a scientist now, and I don't believe in miracles." Others cited "common sense," "logic" or a "lack of evidence" or said simply that they did not believe in God.
Some also rejected organised religion and others mentioned clergy sexual abuse scandals as reasons for quitting church.
Nearly two in ten said they were "spiritual" but not religious.
There were also a significant number who still had a faith but no longer attended church, because they were too busy or simply preferred not to.
Pew Research defines "nones" as atheists, agnostics and those who believe "nothing in particular".
Michael Lipka writes: "Given these different outlooks, it is not surprising that there are major gaps among these three groups when it comes to why they left their childhood religion behind. An overwhelming majority of atheists who were raised in a religion, 82 per cent, say they simply do not believe, but this is true of a smaller share of agnostics, 63 per cent, and only 37 per cent of those in the 'nothing in particular' category."
