How many Muslims live in the United States? Until now, basically, no one has had any idea. By law, the U.S. Census cannot ask questions about religion. There are also plenty of other difficulties in coming up with a number, starting with the problem of defining who is a Muslim: Does one include non-standard believers like Louis Farrakhan and the Druze? Uncertainty has generated some wildly divergent numbers. A large 1990 demographic survey counted 1.3 million Muslims. In 1998, a Pakistani newspaper put the number at 12 million. Even the usually authoritative Yearbook of American and Canadian Churches found 527,000...