The best study on the religious makeup of the United States is The Pew Research Center’s 2021 report on religion in the United States. It shows the changing religious landscape and the increase in secular Americans. Specifically it shows that from 2007 to 2021 the percentage of atheists increased from two percent to four percent and the percentage of agnostics increased from two percent to five percent. The combined total of atheists, agnostics, and Nones grew from16 to 29 percent.

Furthermore, if you look at the answers the Nones gave, 38 percent of them, or 6 percent of the national population, gave answers that sound like those of atheists or agnostics, even if they don’t identify themselves that way. You could add that additional six percent to the official four percent atheists and five percent agnostics for an unofficial total of 15 percent of the population holding atheist or agnostic views.

According to Pew, “The changes underway in the American religious landscape are broad-based. The Christian share of the population is down and religious “nones” have grown across multiple demographic groups: white people, black people, and Hispanics; men and women; in all regions of the country; and among college graduates and those with lower levels of educational attainment. Religious “nones” are growing faster among Democrats than Republicans, though their ranks are swelling in both partisan coalitions. And although the religiously unaffiliated are on the rise among younger people and most groups of older adults, their growth is most pronounced among young adults.”