1980 data were collected by the Glenmary Research Center and include statistics for 111 Judeo-Christian church bodies, including number of churches and adherents. Bernard Quinn, Herman Anderson, Martin Bradley, Paul Goetting and Peggy Shriver supervised the collection. These data originally appeared in Churches and Church Membership in the United States, 1980, published by the Glenmary Research Center.

The studies sponsors invited all Judeo-Christian religious bodies listed in the Yearbook of American and Canadian Churches to participate. Final totals include information from 111 Christian and other religious bodies. The 111 groups reported 231,708 congregations with 112,538,310 adherents, which is 49.2% of the total population of 225,011,986. No attempt was made to count strictly independent churches that have no connection with a denomination.

The RCMS collection reports a measure of members and adherents. Members include only those who are designated as full members by the congregation. Congregational "adherents" include all full members, their children, and others who regularly attend services or participate in the congregation. When religious groups reported only adult membership, the following formula was used to derive the number of adherents: The total county population was divided by the total county population less children 13 years and under (derived from census), and the resulting figure was multiplied by the confirmed members. Using adherents allows for more meaningful comparisons between groups that count children as members (e.g., Catholics) and those that don't (e.g. Baptists).

With the assistance of the United Synagogue of America, the full members (individual adult members) of 793 Conservative synagogues were identified by county. With the assistance of the Union of American Hebrew Congregations, the full members of 708 Reform congregations were also identified by county. No county information was available on either full members or adherents of Orthodox synagogues.

Four black denominations, accounting for 1.8 million adherents, participated in the study. Major efforts were made to enlist the participation of the four other large black churches and the 17 smaller black denominations listed in the Yearbook, but without success. Four Orthodox bodies, accounting for combined adherents of 55,000, participated in the study. Although sizeable efforts were made to obtain data for the remaining 17 groups, statistics were not obtained. Besides the denominations mentioned above, there are 11 non-participating church bodies that reported more than 100,000 to the Yearbook of American and Canadian Churches.

Christian groups in America are often placed into four main traditions: Evangelical Protestant, Mainline Protestant, Historically Black Protestant and Roman Catholic. There is wide variation within each of these four traditions. The most difficult to classify are evangelical and mainline Protestants, with evangelical groups generally being more theologically and socially conservative than mainline groups. Several sources were used for categorizing the many Christian groups into religious traditions, beginning with an article by Brian Steensland and colleagues entitled "The Measure of American Religion: Toward Improving the State of the Art" published in Social Forces (2000, 79: 291-318). This article places most denominations into one of above traditions. For Christian denominations not included in Steensland and colleagues' scheme, two additional sources were consulted: J. Gordon Melton's Encyclopedia of American Religions (8th edition) and Frank S. Mead and Samuel S. Hill's Handbook of Denominations in the United States (10th edition). In addition to those in Steensland and colleagues' classification scheme, separate categories were created for Muslims, Orthodox Christians, Jews, and other groups. The lack of data on historically African American denominations made inclusion of a Black Protestant category unnecessary. Using these sources, staff at the Association of Religion Data Archives (theARDA.com) placed each group into a Religious Tradition.

The 111 religious groups and their category placement are as follows: