Quia.com has put together a list of the Top 10 Largest Religious Groups in America. Check out the list below.
1

Protestantism encompasses the forms of Christian faith and practice that originated with the doctrines of the Reformation
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2

The Roman Catholic Church or Catholic Church is the Christian church church in full communion with the Bishop of Rome, currently Pope Benedict XVI.
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3

Black Christian
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4

Christian (unaffiliated)
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5

Christian Orthodox
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6

A Jew is a member of the Jewish people, an ethnic group originating in the Israelites of the ancient Middle East
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7

A Muslim is an adherent of the religion of Islam
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8

Buddhism is a religion and a philosophy
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9
10

A Hindu, as per modern definition, is an adherent of the philosophies and scriptures of Hinduism, and the religious, philosophical and cultural system that originated in the Indian subcontinent
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