http://usinfo.state.gov/usa/islam/fact2.htm

Islam is one of the fastest-growing religions in the US By the year 2010, America’s Muslim population is expected to surpass the Jewish population, making Islam the country’s second-largest faith after Christianity.1

The American Muslim community is a mosaic of cultures, its members having come from all of the five major continents. In fact, a recent survey showed that most Muslims are immigrants – 77.6% versus 22.4% US born.2

This same survey indicated that the ethnic origins of the Muslim community are as follows:

26.2% Middle East (Arab)
24.7% South Asia
23.8% African American
11.6% Other
10.3% Middle East (Not Arab)
6.4% East Asia

While there are no official population figures for religious affiliation in the United States, experts estimate that there are approximately six million American Muslims. Other estimates range from four to eight million.3

The Britannica Book of the Year estimated that, in mid-2000, there were 4,175,000 Muslims in the United States, 1,650,000 of whom are African American in origin. An average of 17,500 African Americans converted to Islam each year between 1990 and 1995.4

The earliest group of Muslims to arrive in America in significant numbers came from West Africa from 1530 to 1851, because of the slave trade. They comprised an estimated 14% to 20% of the hundreds of thousands of West Africans forcibly removed from their homelands.

The next sizable number of Muslims immigrated to the United States during the early 20th century. They came from Lebanon, Syria and other countries across the Ottoman Empire. 6

The post-World War II era, during the 1960s and ’70s, saw the third substantial wave of immigrants from all parts of the Islamic world. This wave included large numbers of Muslims who came to study at American universities. 7

Approximately a third of American Muslims live on the East Coast (32.2%), 25.3% live in the South, 24.3% in the Central / Great Lakes Region, and 18.2% in the West. 8

There are nearly 2000 mosques nationwide as well as numerous Islamic day schools and Sunday and weekend schools.9

References
1 Carla Power, “The New Islam,” Newsweek, March 16, 1998, p. 34.
2 Source: Zogby International, August 2000, Survey commissioned by the American Muslim Council.
3 Estimates vary widely for all the figures quoted throughout this fact sheet. In terms of overall population, MM Ali reports that there are 6 to 8 million Muslims in America in The Washington Report on Middle East Affairs, May-June 1996, p. 13.
4 Encyclopedia Britannica. “Religious Adherents in the United States of America.” On Britannica.com http://www.britannica.com/. 5 Edward L. Queen, III, Stephen R. Prothero, and Gardiner Shattuck, Jr. The Encyclopedia of American Religious History. (New York: Facts on File, 1996), p. 319.
6 Ibid., P. 320.
7 Ibid.
8 Source: Zogby International, August 2000, Survey commissioned by the American Muslim Council.
9 Omar Khalidi, “Mosque,” In Wade Clark Roof, Contemporary American Religion. (New York: Macmillan, 2000). Also, Yvonne Haddad, “Islam in the United States: A Tentative Ascent; A Conversation,” US Society and Values: The Religious Landscape of the United States, March 1997.