Americans with few or no ties to organized religion are significantly more likely to be male, single, and liberal.
But within this broad portrait researchers are discovering a more nuanced diversity that provides a clearer picture of the nation's "nones," those who claim no religious affiliation on surveys.
For example, atheists and agnostics are generally higher up on the ladder of social class. Those who say they are believers but do not affiliate with a religious group tend to have lower socioeconomic status.
A huge gender gap remains - ranging from 2.6 male atheists for every female atheist to 1.2 actively religious women for every actively religious man.
But there is an exception. Extremely liberal women with graduate degrees are only slightly less likely than extremely liberal men with similar education to be atheists, agnostics or religious nones.
The findings by researchers Joseph Baker of East Tennessee State University and Buster Smith of Catawba College in their new book "American Secularism." Their work is part of an increasing effort by scholars to learn more about nones and their potential for reshaping the religious-secular landscape.
There are challenges to the continued growth of religious nones. These include their low birth rates, a relative lack of institutional organizations and an enduring cultural bias against nonbelievers, atheists in particular, Baker, Smith and other analysts note.
But there are also prospects for continuing growth as younger and younger generations become more likely to forgo identifying with a religious group.
"Regardless of what one makes of the increasing visibility of secularity or the persistence of traditional religious perspectives," Baker and Smith state, "both are here to stay."
The rising number of people reporting no religious ties in major surveys are striking.
Eight percent of Americans said they had no religious preference in the 1976 General Social Survey; just under 21 percent reported they were nones in 2014. The Pew Religious Landscape Survey found the percentage of adults reporting no religious affiliation rose from 15 percent in 2007 to just under 20 percent in 2012.
Whether this represents a proportionate advance in secularization is open to interpretation.
For example, two-thirds of nones said they believe in God and one-third said religion is at least somewhat important in their lives, according to the 2012 Pew survey.
In their new book, Baker and Smith analyze the data from the General Social Survey, Pew, the World Values Surveys and other sources and declare "the time has come to cease understanding the U.S. as 'exceptionally' religious."
They refer to the current growth in nones as "The Great Abdicating," evoking comparisons with the historical periods of religious revivals in U.S. history known as The Great Awakenings.
At a spring symposium at Baylor University, several scholars spoke of the vibrancy of American religion, with many Americans more likely to see their faith in personal as opposed to institutional terms.
When Americans are grouped into the category of "nones," "It doesn't mean that they are not a member of a church, and it doesn't mean that they don't go to church, it doesn't mean that they don't pray, and it doesn't mean that they don't have a sense of the divine in their lives." religious historian J. Gordon Melton said.
His take: "You're living in one of the most religious countries that has ever existed on the face of the Earth."
Looking to the future
There is greater consensus that younger generations are increasingly loosening their ties with organized religion.
About a third of adults under age 30 have no religious affiliation, according to the 2012 Pew survey.
Several studies have indicated religion increases with age, with many returning to more active faith lives as they get married and have children. Contemporary cultural trends of young adults delaying marriage or embracing a single lifestyle may in part account for their lack of affiliation.
A new study exploring generational trends in religion using 35 years of survey data from 420 four-generation families found "an upward drift in religious intensity and strength of beliefs" as people aged.
But the research also provides evidence younger generations appear to be defining religious beliefs in new ways.
In-depth interviews with 157 people from 25 families indicated Millennials are more likely to separate spirituality from religion and they are more likely to view the divine as personally present in their lives.
"Time will tell how these diverse generational cohorts, and younger ones to follow, will continue to amplify the religious practices and institutions of preceding generations' religion, and what this implies for adults in late life," said researchers from the University of Southern California and Syracuse University.
In any scenario, research is making clear that any analysis has to take into account the wide diversity of beliefs and practices of those who do not report a particular religious affiliation.
One of the first enduring stereotypes that can be dismissed, Baker said, is the tendency of many to equate nones with atheists despite survey results indicating only about 3 percent of Americans self-identify as atheists.
"Atheism remains kind of shorthand for secularism," he said.
Yet many among those reporting no religious affiliation reveal a wide variety of beliefs and practices, often finding themselves somewhere between the categories of religious and secular.
For example, more than half of the religiously unaffiliated in the Pew survey said they think of themselves as either a religious person or spiritual but not religious.
Maybe it is even time to stop calling them nones.
Image by Thomas Lefebvre [CC0 Public Domain], via Pexels
Image by Joshua Earle [CC0 Public Domain], via Pexels