Excerpt from the text at the above link (emphases mine):
There are between 6 and 7 million Muslims in America today. In other words, Muslims outnumber some Christian denominations and are equal to the number of Jews. Research done in the year 2000 by prominent American universities and Islamic foundations show that the number of Muslims is increasing rapidly and that Islam is growing stronger day by day.Much more at this link, including access to additional pages.
The above graphic representation shows the rising numbers of mosques in America.
The main theme of this research, known as the Mosque Study Project, is the establishment of mosques in America. The reason for this is that mosques occupy a very special place in any statistical compilations done with regard to the American Muslim community. Mosques in America are both houses of worship and gathering places for talking with one another and launching cultural activities to make Islam more widely known. Every mosque establishes a relationship with the press to introduce Islam to a wider audience, speaks with local politicians, visits schools and churches, engages in interfaith dialogue and carries on other such activities. Thus, research done on these mosques is one of the most useful tools for gathering accurate and enlightening information on this community's state.
According to this research, America now has about 1,209 mosques, most of which were constructed very recently. Thirty percent of these mosques were built in the 1990s, and 32% were built in the 1980s. Other statistics show that in 1994, the total number of mosques in America was 962; in 2000, there was a 25% increase in this number.
These data show a natural parallel with the growing number of Muslims. For example, according to determinations made in 1994, the number of Muslims attending mosque services was 500,000; in 2000, this figure had increased to 2 million-an approximately 300% increase. A significant part of this number is composed of people who converted to Islam. The same research shows that about 30% of those worshippers are converts. According to these data, about 20,000 Americans accept Islam every year....
Also see my recent posting "Not A Surprise To Those Of Us Who Watch."