This guide lists encyclopedia and bibliographic resources for the study of American church history, including both Catholicism and Protestant denominations.
The ARDA Data Archive is a collection of surveys, polls, and other data collected by researchers, including U.S. church membership, and denominational surveys inter alia.
Churches and Church Membership in the U. S., 1990 by 
Report on Statistics of Churches in the United States at Their Eleventh Census, 1890 (Classic Reprint) by