A new comprehensive study of religious congregations in the United States has resulted in a detailed look at the most -- and least -- religious counties in the country.

The 2010 U.S. Religious Census: Religious Congregations & Membership Study, released this month, features a county-by-county assessment on congregations, members, adherents and attendance for 236 different faith groups.

Of metropolitan areas with populations over 1 million, Salt Lake City was deemed the most religious, with nearly 74 percent identifying as religiously adherent (defined as "all those within a congregation," including members, children and attendees who are not members). At the other end of the spectrum was the Portland, Ore. area with just 32 percent identifying as such.

The following map shows a higher concentration of religious adherence (55 percent or higher, yellow and orange colors) in counties the Midwest and South, and a lower concentration (0 to 44.9 percent, blue and green colors) in counties in the West and Northeast.

Get charts of the study's breakdown of counties by faith group here.