Source: The Martin Marty Center
http://marty-center.uchicago.edu/sightings/archive_2005/0926.shtml
On September 26, 2005 The Martin Marty Center at the University of Chicago reported, "C. Kirk Hadaway and Penny Long Marler [released new data on worship in America in their report entitled:] 'How Many Americans Attend Worship Each Week? An Alternative Approach to Measurement' (Journal for the Scientific Study of Religion, September 2005)... The two authors do their best to estimate the number of churches and other houses of worship, converting careful local samplings to national totals. They estimate that there are 331,000 congregations distributed over the United States... [Among other denominational findings, the report stated that] at those 331,000 congregations, on average there were 161.9 in attendance, or 20.4 percent of their constituencies, totaling 53,603,588... The significance of their measurement, say the authors, is that 'only around 21 percent of the American population attend religious services during a typical week -- a figure that is exactly half of the most often reported Gallup poll total of 42 percent.'"