The U.S. government estimates the population at 21.3 million (midyear 2020 estimate). According to a 2011 government census, ROC adherents constitute 86.5 percent of the population and Roman Catholics almost 5 percent. According to the census, there are approximately 151,000 Greek Catholics; however, Greek Catholics estimate their numbers at 488,000. According to the Greek Catholic Church, since the time of the census, a significant number of persons whose Greek Catholic families were forced to covert during the Communist regime rediscovered their roots and joined the Greek Catholic Church. Other religious groups include Old Rite Russian Christians; Protestants, including Reformed Protestants, Pentecostals, Baptists, Seventh-day Adventists, Evangelical Lutherans, and Evangelical Augustans; Jews; Muslims; Jehovah’s Witnesses; Baha’is; The Church of Jesus Christ of Latter-day Saints; Zen Buddhists; the Family (God’s Children); the Family Federation for World Peace and Unification (Unification Church); the Church of Scientology; and the International Society of Krishna Consciousness. Atheists and nonbelievers represent less than 1 percent of the population.

According to the 2011 census, Old Rite Russian Christians are mainly located in Moldavia and Dobrogea. Of the 64,337 Muslims accounted for in the 2011 census, 43,279 live in the southeast near Constanta. Most Greek Catholics reside in Transylvania. Protestants of various denominations and Roman Catholics reside primarily in Transylvania. Orthodox and ethnic Ukrainian Greek Catholics live mostly in the north. Orthodox ethnic Serbs are primarily in Banat. Members of the Armenian Apostolic Church are concentrated in Moldavia and the south. Virtually all members of the Protestant Reformed and Unitarian Churches of Transylvania are ethnic Hungarians. More than half of the Roman Catholic and Evangelical Lutheran Churches in Transylvania are composed of ethnic Hungarians. Approximately 40 percent of the country’s Jewish population of 3,400 resides in Bucharest.