Religious Data
The Association of Religious Data allows you to interactively explore the highest quality data on American and international religion using online features for generating national profiles, maps, church membership overviews, denominational heritage trees, tables, charts, and other summary reports. Over 350 data files are available for online preview and most can be downloaded for additional research. I had a question about the number people practicing Islam in parts of New York for a question about the dietary practice known as halal . I used The ARDA search mechanism and found files describing the number of Muslims by county. Other sources of religious data: Hartford Institute for Religion Research and Glenmary Research - the latter especially good for a breakdown of Roman Catholic numbers. Not so incidentally, it would be a mistake to assume that most U.S. Arabs are Muslims. In fact, if you go here , you'll see that most Arab-Americans are Christians.