Download the 1994 Mosque Report done by Ishan Bagby. This is the first of several profiles of US Mosques he did.
Dr. Bagby generated a similar study in 2000. You can download the full report at http://www.cair.com/portals/0/pdf/The_mosque_in_America_A_National_Portrait.pdf
In February 2011 he and co-researchers will release a 2010 study of over 500 Mosques in the United States.