The U.S. has been steadily losing its religion for decades. For the most part, Protestants have been leaving the church while the affiliation rates among Catholicism and other religions in the country have remained stable. But since 1990, Americans have been abandoning both belief and religious affiliation at such a fast pace that, by 2035, it's likely that 35 percent of the population will have no religious affiliation — outnumbering protestants.
According to the Theory of Secularization, as societies become more modern, they become less religious. Aspects of secularization include decreasing participation in organized religion, loss of religious belief, and declining respect for religious authority. Until recently the United States has been a nearly unique counterexample, so I would be a fool to join the line of researchers who have predicted the demise of religion in America.
- The fraction of people with no religious affiliation has increased from less than 10% in the 1990s to more than 20% now. This increase will accelerate, overtaking Catholicism in the next few years, and probably replacing Protestantism as the largest religious affiliation within 20 years.
- Protestantism has been in decline since the 1980s. Its population share dropped below 50% in 2012, and will fall below 40% within 20 years.
- Catholicism peaked in the 1980s and will decline slowly over the next 20 years, from 24% to 20%.
- The share of other religions increased from 4% in the 1970s to 6% now, but will be essentially unchanged in the next 20 years.
Though organized religion may be seeing a downturn, the notion of 'spiritual but not religious' is gaining traction:
A 2014 Pew study found that, between 2007 and 2014, the percentage of Americans who felt a "deep sense of spiritual peace and well-being" had increased from 52 to 59 percent, while the percentage of those who felt a"deep sense of wonder about the universe" increased from 39 to 46 percent.