Historical Statistics of the United States: Millennial Edition
This online book provides nation-level data and is an excellent source for background information. It includes both tables and essays. This resource will help you understand the context of historical trends and the nature of data collection on a specific topic. See Chapter Bg, "Nonprofit, Voluntary, and Religious Entities."
The U.S. Census Bureau conducted 4 censuses of religious bodies from 1906-1936. The adoptation of Public Law 94-521 prohibits the Census Bureau from asking mandatory questions about religious affiliations. For a complete overview of Census Bureau publications about religion, please visit the Question & Answer Center topic Religion: Data Sources.