The term was first applied to the West Coast of the United States in 1985 by Rodney Stark and William Sims Bainbridge, who found that California, Oregon, and Washington had the United States' lowest church membership rates in 1971, and that there was little change in this pattern between 1971 and 1980. Since 1980, however, California's church membership rate has increased; in 2000, the state had a higher percentage of church members than several states in the Northeast and Midwest. Some religious groups are under-counted in surveys of religious membership.
As of 2000[update], the six U.S. states reported to have the lowest rate of religious adherence were Oregon, Washington, Alaska, Nevada, Maine, and West Virginia. Although West Virginia is reported to have a low rate of religious adherence, it is above the national average rate of church attendance. Sociologist Samuel S. Hill, comparing data from the North American Religion Atlas and the American Religious Identity Survey, concluded that a "disproportionately large number of West Virginians" were not counted. In 2006, Gallup reported that the lowest rates of church attendance among the 48 contiguous states were in Nevada and the New England states of Connecticut, New Hampshire, Vermont, Rhode Island, Massachusetts, and Maine. Church attendance in the western states of Oregon, Washington, and California was only slightly higher. A 2008 Gallup poll comparing belief in God among U.S. regions found that only 59% of residents in the Western United States believe in a god, compared to 80% in the East, 83% in the Midwest, and 86% in the South.
There has been debate as to whether the Western United States is still the most irreligious part of the United States, due to New England surpassing it as the region with the highest percentage of residents unaffiliated with any religion. On a state level, it is not clear whether the least religious state resides in the New England area or the Western United States, as the 2008 American Religious Identification Survey (ARIS) ranked Vermont as the state with the highest percentage of residents claiming no religion at 34%, but a 2009 Gallup poll ranked Oregon as the state with the highest percentage of residents identifying with "No religion, Atheist, or Agnostic", at 24.6%.
- Finke, Roger; Scheitle, Christopher (2005). "Accounting for the Uncounted: Computing Correctives for the 2000 RCMS Data". Review of Religious Research 47 (1). Retrieved 2011-12-12.
- Wright, Richard A (1986). "Reviewed work(s): Big Structures, Large Processes, Huge Comparisons by Charles Tilly". Annals of the American Academy of Political and Social Science 484: 184–185.
- "All Denominations--Rates of Adherence Per 1000 Population (2000) *Adjusted*". The Association of Religion Data Archives. Retrieved 2009-01-16.
- Newport, Frank (April 27, 2006). "Church Attendance Lowest in New England, Highest in South". Gallup. Retrieved 2010-01-22.
- "North American Religion Atlas". Indiana University Purdue University-Indianapolis.
- Wilson, Charles Reagan & Mark Silk (eds.), Religion and Public Life in the South: In the Evangelical Mode, AltaMira Press, 2005, pg. 151. ISBN 0-7591-0635-5
- Newport, Frank (July 28, 2008). "Belief in God Far Lower in Western U.S.". Gallup. Retrieved 2010-01-22.
- Lin, Joanna (March 16, 2009). "New England surpasses West Coast as least religious region in America, study finds". Los Angeles Times. Retrieved 2010-01-22.
- Kosmin, Barry A. et al (2009). "American Religious Identification Survey (ARIS 2008)". Trinity College. Archived from the original on 2011-04-15. Retrieved 2010-01-22.
- Kosmin, Barry A. et al (2009). "American Nones: The Profile of the No Religion Population". Trinity College. Retrieved 2010-01-22.
- Newport, Frank (August 7, 2009). "Religious Identity: States Differ Widely". Gallup. Retrieved 2010-01-22.
- 2000 Map of Religious Adherents as a percentage of population in the United States
- Map Gallery of Religion in the United States