Social Explorer creates maps and reports of religious congregations based on the Religious Congregations and Membership Study for 1980, 1990, 2000 and has 2009 data from the InfoGroup American Church Lists.
This comprehensive resource is more than just a data archive! Also included are National Profiles, reports and maps of U.S. Congregational Membership, information on Denominations, QuickStats from major national surveys, ranked lists of religious groups, maps, and a Learning Center.
Adherents.com is a collection of more than 41,000 "adherent statistics and religious geography citations." It provides access to statistics on religious groups broken down by geographical area and by name of faith group.
Disclaimer: Watch out for ads and dubious links. Stick to the Main Statistical Database which includes citations to bibliographic sources to substantiate the statistics.
Statistics on religion, like most other statistics, must be interpreted with a critical eye. Data on religion may be reported at either the insitutional level or the individual level. That is, there are surveys of religious insitutions themselves and there are surveys of individuals and their self-reported attitudes and affilitiations. Keep in mind that surveys of religious institutions are also self-reporting, so over-reporting of membership is more likely that under-reporting. The diversity of religious organizations and varying definitions of membership can also have an effect on comparing membership numbers among different organizations. Some organizations may not share reports with the public, or even keep numbers. There has been no government-mandated count of religious organizations since the last Religious Bodiescensus taken in 1936.
Most of the resources that you encounter in this guide will have a disclaimer explaining the collection method and nature of the data. Be sure to read this section!
Browse to bottom of Section 1. Population, or use the search feature. Includes tables on Self-Described Religious Identification Of Adult Population, Religious Adherents And Jewish Population by States, Religious Adherents By Metropolitan Area Status And Religious Groups, Religious Bodies-Selected Data (from the 2015 edition).