I'm interested in historical trends in religion and wondered if anyone knows of any reasonable sources of data on the number of adherents, for any/all different religions, throughout human history.

Obviously, older numbers would be very approximate estimates - and modern numbers would also likely be rough, given that this is a personal matter and somewhat sensitive in some parts of the world.

Does this information get included in census data - or has it ever been in the past? Do you know of any sources of data on this, even for single periods or religions, that I could use to piece together a fuller picture?

I know about this, which is great, but fairly recent and major religions only. Anything older, covering more religions?

  • No. There are no reasonable sources of information regarding adherents. Religiosity and observance are so highly contextual that this is unanswerable. Jun 25, 2013 at 8:05
  • Apart from saying 'self-identified' - which would suit my purposes - might there also be a narrower definition of 'adherant' that might make this more tractable? Jun 25, 2013 at 8:21
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    I'd say it was about 42% adherents, 42% non-adherents, and the rest somewhere in between ... (note-to-self: a "42" tag could be useful for questions that insist on a quantitative answer where there is perhaps none ... :)
    – Drux
    Jun 25, 2013 at 9:59
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    Yes, @DuncanLock, that is precisely the point. See Philip S. Gorski (2000) "Historicizing the Secularization Debate: Church, State, and Society in Late Medieval and Early Modern Europe, ca. 1300 to 1700" American Sociological Review (65:1) Special Issue: "Looking Forward, Looking Back: Continuity and Change at the Turn of the Millenium" pp. 138-167 jstor.org/stable/2657295 Jun 25, 2013 at 10:13
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    @DuncanLock Instead of looking for numbers of religious adherents, you might have better luck looking at the numbers of places of worship (churches, mosques, synagogues, etc) over time. Since they would be kept on various tax/ownership records, you might find some interesting data with a little digging.
    – Gwen
    Jul 25, 2013 at 21:32

1 Answer 1


Here is one data point (from Jakob Burckardt's The Age of Constantine the Great) presumably among very many and already self-contradictory (translation courtesy of Google :)

The last time of Diocletian and Maximiam has come through the torture and blood streams of the great persecution of Christians into a horrible reputation. It has tried in vain to determine the amount thereof and the number of victims even close, so it has no basis each calculation, namely a reliable date on the number of existing at all at that time in the Roman Empire Christians. After Staudlin they accounted for half of the total population, according to Matter fifth, according to Gibbon merely one-twentieth, one-twelfth to La Basti, which perhaps comes closest to the truth.

As also indicated in my earlier comment, IMHO you can't hope for any definite answer to a question such as this one, the more so the "older" any conceivable numbers may get.

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