The map of religious adherence in the United States defies some common perceptions. Membership in a religious organization, for example, is shown as higher rate in southern New England than in the eastern part of the so-called Bible Belt. The data used to make these maps, however, are not necessarily accurate, and they do not measure the intensity of religious belief. 
Religious adherence, moreover, has been declining almost everywhere over the past several decades. But the basic patterns depicted in these maps are still worth examining. As they show, membership in an organized faith is highest in the central part of the country, especially the northern and southern Great Plains, and in the LDS (Mormon) region of Utah and eastern Idaho. It is lowest in central Appalachia and the greater Pacific Northwest, including western Montana. Colorado, Maine, and the lower peninsula of Michigan also have low rates of membership. In the southeast, religious adherence is low in counties with large Black populations.
Montana is revealed as a religiously divided state. Many counties in the northeastern and north-central parts of the state have very high adherence rates, while many in the west-central and south-central regions have very low rates. Demographic history plays a role here. Northeastern 
Montana was heavily settled by Norwegian farmers, a group that historically had high rates of (Lutheran) religiosity. In several northeastern counties, Lutheranism is still the dominant faith. Most of the first Euro-American settlers in the rest of Montana were ranchers and miners, groups that generally had low rates of adherence. In the copper counties of Silver Bow (Butte) and Deer Lodge (Anaconda), however, relatively devout Irish Catholic workers later gained demographic domination. These are now the most religious counties in the western part of the state.
Roman Catholicism has been historically mapped as the leading faith over almost all Montana except the northeastern Lutheran belt. More recent maps, however, show Mormonism as the top religion 
of several western counties. These areas have not historically been mapped as part of the LDS cultural 
zone. More recently, 
geographer Paul F. Starrs has remapped the Mormon cultural region to account for its expansion. He now includes southwestern Montana’s Beaverhead Country within its outer sphere. More than 11 percent of Beaverhead’s residents belong to the LDS church. Statewide, the figure is roughly five percent, making it Montana’s second largest faith (after Roman Catholicism). Montana currently 
has the country’s seventh highest percentage of LDS member – or eighth, if one includes territories (American Samoa).