Surveys show that Americans without a religious affiliation (which include 'nothing particular', agnostic, and atheist), sometimes referred to as "Nones" range around 23.8%,
[3] 26%,
[2] 24.8%,
[4] 33%,
[5] 21%,
[6][7] and 31.4%
[8] of the population, with 'nothing in particulars' making up the majority of this demographic.
Since the early 1990s, independent polls have shown the rapid growth of those without a religious affiliation.
[9][10][11]
Identifying as religious and/or spiritual vary widely across surveys depending on the wording they use. Among longitudinal academic surveys such as the General Social Survey which allows for degrees of religious identification: 21.5% are not religious, 25.1% were slightly religious, 37.5% were moderately religious, and 15.5% were very religious in 2018.
[12] According to a 2017 Pew report which asked about religious and spiritual identification: 54% of Americans consider themselves religious, 75% consider themselves spiritual. In combination, 27% are spiritual but not religious and another 18% are neither spiritual nor religious. Those who do not consider themselves as 'religious' may often consider themselves "affiliated" with a major religion and/or "spiritual".
[1] According to Pew in 2017, 72% of the "Nones" believe in God, a higher power, or spiritual force.
[13]
Self-identification among the Nones is also diverse. For instance, according to Pew study in 2009, only 5% of the total US population did not have a belief in a god. Out of all those without a belief in a god, only 24% self-identified as "atheist", while 15% self-identified as "agnostic", 35% self-identified as "nothing in particular", and 24% identified with a religious tradition.
[14] According to the Pew Research Center in 2014, self-identified atheists were 3.1% and agnostics were 4%,
[11] and by 2019, self identified atheists were 4% and agnostics were 5%.
[2] According to the 2014 General Social Survey, 3% identified as atheists and 5% identified as agnostics.
[15]
https://en.wikipedia.org/wiki/Irreligion_in_the_United_States
https://www.pewforum.org/religious-landscape-study/religious-family/atheist/