"Muslim Journeys | Item #169: Distribution of Muslim Population in the United States, 2010."
"The percentage of Muslims in each U.S. county is shown in a 2010 map. Concentrations range from 5 percent in a few counties to 0 percent, reported in most counties. It should be noted, however, that the data used for this map was collected through surveys of mosques; consequently, Muslims residing in counties without mosques may not have been counted. Estimating the membership of any faith group in the United States is challenging, since census data does not record this information, and many people who identify with a particular religion do not attend houses of worship regularly."