Religious Congregations & Membership Study.
The 2010 U.S. Religion Census: Religious Congregations & Membership Study (RCMS) is a county-by-county enumeration of religious bodies in the US. A quick overview is available here. It is an update of the 1952, 1971, 1980, 1990, and 2000 studies originally done by the National Council of Churches and the Glenmary Research Center.
