The U.S. government estimates the total population at 67.6 million (midyear 2019 estimate). The law prohibits government collection of data based on race, ethnicity, or religion. However, a wide range of unofficial statistics and studies circulate.

A report released in July by the Observatory for Secularism, a government-appointed commission, in cooperation with polling company Viavoice, presented estimated figures of those who identified as part of a religion or felt tied to a religion. According to the report, whose figures are consistent with other estimates, 48 percent of respondents identify as Catholic, 3 percent Muslim, 3 percent Protestant, 2 percent Buddhist, 0.7 percent Jewish, 0.6 percent, and 1 percent other religion; 34 percent said they have no religious affiliation and 7 percent preferred not to respond. The same report estimates “other” religions’ numbers as follows: Jehovah’s Witnesses, 140,000-250,000, and Hindus, 150,000-300,000. In addition, the observatory’s report stated 31 percent consider themselves nonbelievers or atheists.

The report stated the number of residents linked to Islam in the poll was likely underestimated, as some Muslim and Muslim-affiliated residents may have declined to state their religion. According to the report, the “most precise” estimate of the Muslim population, based on multiple polls and demographic extrapolation, is likely between 3.3 and 5.0 million residents. The report stated the Muslim population corresponds with the arrival of immigrant populations, particularly from the Mediterranean and West Africa. The report also tied Hindu and Buddhist populations to immigrant communities.

The report attributes the growth in the Protestant community, from 2.5 percent of the population in 2010 to 3.1 percent during the year, to the growing number of Evangelical Christians, who number approximately one million.