Turns out you all are pretty interested in religion statistics.
Hundreds of thousands of people read our last article on the U.S. Religion Census, and, in particular, what it said about the state of membership in The Church of Jesus Christ of Latter-day Saints in 2020. At the end of that story was a promise: We’d also look at how those membership numbers have changed over time.
To do so, we’re going to look at five editions of the U.S. Religion Census, every decade since 1980. This study tracks numbers on a county-by-county basis for all religions, data that can be difficult to find elsewhere.
But first, let’s look again at the methodology of how the U.S. Religion Census works.
U.S. Religion Census methodology — and how it’s changed over time
Since 1990, the U.S. Religion Census is compiled by the Association of Statisticians of American Religious Bodies (ASARB) every 10 years. We also include 1980 data here, thanks to a similar census from the Glenmary Research Center.
In our previous article, we explained how that approach has worked: in short, the ASARB contacts the various denominations and churches, small and large, and asks them how many adherents they have. Adherents, to the ASARB, is defined widely as all people with an affiliation to a congregation (including children, members and attendees who are not members).
This means that each group is responsible for its own standards in reporting that accurately. As we pointed out, that can lead to mistakes or inflated numbers — as we discovered when the LDS Church reported more Latter-day Saints in northern Utah’s Rich County (2,763) than there were residents in that county (2,510) in 2020.
Furthermore, the Salt Lake City-based faith has shifted how it reports adherents to the census. Pennsylvania State University researchers who studied the U.S. Religion Census changes over time explain: For the 1980-2000 collections, the LDS Church-reported total “did not include members who, though baptized, were not at the time associated with a specific congregation.” For the 2010 and 2020 collections, the church “changed its procedures to include the previously excluded baptized persons, a figure more consistent with what it has reported elsewhere and more comparable to how other denominations count adherents in the religion census.”
In short, this creates a jump in the number of adherents reported in the past two tallies. In the 2000 collection, for example, the church’s smaller figure reported in the U.S. Religion Census was 4,224,026 adherents nationwide. Meanwhile, its more inclusive number, which it would have reported under the new methodology, would have been 5,208,827. This is a 23% spike, just by altering the definition of who is an adherent.
This isn’t fraudulent or anything. As the Penn State researchers note, other religions are doing this, too. It does, however, create differences in the data between 1980 and 2000 and the years after bigger than what reality would reflect.
OK, enough set up. What do we see in the data?
Utah membership
Here’s how the number of Utah Latter-day Saints has changed in the U.S. Religion Census since 1980.
So, in the state, we see big growth in the overall number of Latter-day Saints. However, there’s more of a recent flatline, or even a small decline, as we look at the number of Latter-day Saints as a percentage of the state’s total population.
But remember, the biggest strength of the U.S. Religion Census is the county-by-county data over time. What do we see there? For online readers, be sure to click the drop-down in the graphic to select the county.
Utah’s five most-populated counties all show downturns in the percentage of residents whom the church considers adherents in the past decade. In Salt Lake County or Summit County, that decrease has been part of a longer, decadeslong trend; in Utah County, that dip is more recent.
Here’s one that surprised me: In 17 of Utah’s 29 counties, there’s been a decrease in even the reported absolute number of Latter-day Saints between 2010 and 2020. Meanwhile, in 27 counties, the non-Latter-day Saint population has grown.
Only three counties have seen an increase in the percentage of their residents who were reported as Latter-day Saints: Box Elder, Garfield and Rich.
Again, I’m a little surprised that this is happening despite high (though falling) birthrates among Latter-day Saints generally. With all the factors involved, I don’t dare speculate on the reasons for these trends, other than to note that the data shows declining U.S. religiosity overall.
Andy Larsen is a data columnist for The Salt Lake Tribune. You can reach him at alarsen@sltrib.com.
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