Americans have less faith in organized religion than they did nearly a decade ago, a new study shows.

A staggering 21 percent of those surveyed said they don’t practice a “formal religion” — up from the 15 percent who said that in 2008, according to Gallup.

“Religion is losing influence in society,” according to Gallup, which did not offer a reason for the decline. “This may be a short-term phenomenon or an indication of a more lasting pattern.”

Overall, 74 percent of Americans identified as Christian and 2.1 percent said they were Jewish; 1.8 percent said they were Mormon and .8 identified as Muslim, according to the pollsters.

Everyone else either claimed to be “none/ atheist / agnostic” or gave no response at all, researchers said.

The number of true believers has dropped dramatically since the 1940s and 1950s, when less than 3 percent said they practiced no formal religion.

In those decades, 90 percent of Americans identified as Christian — and nearly everyone else said they were Jewish, according to past Gallup surveys.

It wasn’t until the 1970s that the number of Americans practicing no religion began to grow, rising to 10 percent that decade. By the 2000s, that percentage climbed to the teens.

Even among the faithful, church attendance is also lower than it has been in past decades, the study shows. Roughly 36 percent of Americans attend, down from 41 percent in 1939, the first year the study was conducted.

The poll surveyed 173,229 Americans and was conducted between Jan. and Dec. 2016