The decadal U.S. Religion Census is a collaborative effort of religious groups around the country. The research team, who are all members of the ASARB association, contact formal denominations and religious groups around the country and request their congregational counts, attendance and membership by county. Additionally, certain groupings of religious communities without formal national headquarters are included through the use of special data collection studies. For each decade of the Census, a listing of participating groups and the methodology for the special collections are given as well as challenges and caveats regarding the use of this data.