(Photo by Charles McQuillan/Getty Images)

(CNSNews.com) -- A new survey shows that the percentage of Americans who belong to a church, synagogue, or mosque has fallen 20 points since 1999 to an average of 50%. In addition, among Millennials, only 42% say they belong to a church.

In the survey, Gallup asked, "Do you happen to be a member of a church, synagogue or mosque?" Fifty percent of Americans answered yes. Back in 1999 that percentage was 70%.

Gallup's data show that between 1937 and 1976, church membership in America "was 70% or higher," and then hit 68% from the late 1970s through the 1990s. It has fallen dramatically over the last 20 years, 1999 to 2019.

On a related note, Gallup reported that in 1998-2000 some 90% of Americans said they had a "religious affiliation" and only 8% said they had "no religion." Today, in 2016-2018, Gallup found that 77% of Americans claim a religious affiliation but 19% say they have "no religion."

The percentage of Americans claiming no religion has more than doubled in 20 years.

"It is clear then, that the nature of Americans' orientation to religion is changing, with fewer religious Americans finding membership in a church or other faith institution to be a necessary part of their religious experience," said Gallup.

The polling firm further reported that "older Americans [are] far more likely than younger adults to be members of churches. However, church membership has dropped among all generational groups over the past two decades, with declines of roughly 10 percentage points among traditionalists, baby boomers and Generation X."

"Most millennials were too young to be polled in 1998-2000," said Gallup. "Now that they have reached adulthood, their church membership rates are exceedingly low and appear to be a major factor in the drop in overall U.S. church membership. Just 42% of millennials are members of churches, on average."

For comparison, 68% of Traditionalists (born in 1945 or before) claim church membership today, as do 57% of Baby Boomers (born 1946 to 1964), and 54% of Generation X (born 1965-1979). However, even in those groups, church membership is down about 10% each since 1998.

(Photo by Sean Gallup/Getty Images)

"Although the United States is one of the more religious countries, particularly among Western nations, it is far less religious than it used to be," reported Gallup. "Barely three-quarters of Americans now identify with a religion and only about half claim membership in a church, synagogue or mosque."

"The rate of U.S. church membership has declined sharply in the past two decades after being relatively stable in the six decades before that," said the polling firm. "A sharp increase in the proportion of the population with no religious affiliation, a decline in church membership among those who do have a religious preference, and low levels of church membership among millennials are all contributing to the accelerating trend."