Published by the Cooperative Congregations Studies Partnership, Faith Communities Today conducts a series of ongoing studies related to congregational life. Their data looks at trends across many different sects of Christianity and also interfaith worship. The most recent study was conducted in 2010.
The NCS surveys a representative sample of America's churches, synagogues, mosques and other local places of worship. It gathers information about a wide range of characteristics and activities of congregations.
Provides a county-by-county measure of religious bodies in the US. The study is currently sponsored by the Association of Statisticians of American Religious Bodies. The survey includes maps, reports, and data sets of survey results. 2010 RCMS was released May 1, 2012. An overview of the study can be found here. Full regional reports can be searched through the ARDA.
The US Congregational Life has been conducted in two waves in an effort to take a "snapshot" of regular congregational life. The survey was conducted by worshipers in a random sampling of congregations in the US. Results of the survey are made available, along with publications utilizing the data, in the Of General Interest section of the Publications and Research link on the main page, generally arranged by topic. Findings of this survey are also found in Woolever's Field Guide to US Congregations.