According to the Barna Group the “percentage of adults nationwide who have attended a church [worship] service in the past seven days” in 2004 was 43%” (1)
The University of Michigan found that “weekly church attendance is higher in the United States than in any other nation at a comparable level of development […]. Fully 44 percent of Americans attend church once a week […] compared with 27 percent of people in Great Britain, 21 percent of the French, 4 percent of Swedes and 3 percent of Japanese. Moreover, 53 percent of Americans say that religion is very important in their lives, compared with 16 percent, 14 percent, and 13 percent, respectively, of the British, French and Germans.” (2)
1 http://www.barna.org/FlexPage.aspx?Page=Topic&TopicID=10
2 http://www.umich.edu/news/index.html?Releases/1997/Dec97/chr121097a