Not really a question that can be sourced, so this is all anecdotal

It seems to depend on the field. I know a Catholic medievalist who has told me that other religious folks (mostly Catholic) are more common among medievalists than among, say, historians of early modern Europe.

I've also noticed that there seem to be more Christians studying the 'biblical' eras, which makes a certain amount of sense.

Overall, historians seem more irreligious than the general population, but less so than, say, physicists.

Not a historian, but an archaeologist- I'm one of the very few even slightly religious folks in my field. It's not surprising, in the American anthropological archaeology, that this is case. It's hard to be an apathetic believer when your discipline preaches cultural relativism.

The interesting thing is that I've found myself shifting strongly to a more traditional, conservative Christian mindset (i.e. that of Catholics and traditional Lutherans and Anglicans) and away from the contemporary, Americanized faith I grew up in. In modern protestant and reformed circles, there's a lot of effort to kind of integrate with the public. This occurs quite frequently in regards to church functions: us Lutherans love poking fun at the "latte-Baptists" with their early-30s, gottee-ed, flannel shirted dude on a metal stool with a latte in one hand making painful attempts at connecting with hip high schoolers. We understand the attempts, and if they should work, all the better for you. But we also see it in their approaches to academics. My friends and family are always bringing up yet another time they found Noah's Ark on "Mount Ararat." I grew up watching Ken Ham's videos in science class, where they told me that, had they lived millions of years ago, the dinosaurs would have fallen off the earth because it spun too fast. It's always felt like they were desperately grasping for scientific and historical evidences to bolster their faith, as if if they found enough facts they could prove once and for all that they were right.Now not only do I find this kind of societal integration un-Biblical, I also find it increasingly obnoxious. Our faith is based on some guy who turned water into wine, walked on water, died, and came back to let his friend stick his fingers through his stab holes. I don't think the irreducible complexity of a flagellum can even come close to reproducing those scientifically. Catholics, Lutherans, etc. simply respond "Well, you ain't seen nothing yet." It's weird, magical, supernatural, and intrinsically non-scientific, and we're not gonna try to hide that- in fact, we're proud of it.

Again, an anecdotal response.

As has been said, religion among medievalists seems quite common, maybe less so among those who study late antiquity, unless they are specifically interested in Patristics. I also know a number of early modernists who are committed Catholics, and study Catholic recusancy.

In general, academic life (at least in the UK) can be pretty secular. A member of the theological faculty at the University of Oxford who is also a Catholic priest once told me that university colleagues often treated him as though he were dishonest - being a clever man, they thought, he couldn't actually believe all that mumbo jumbo.

Many of my history profs were religious, one was Catholic (European history), another Orthodox (European history), a Baha'i' (Southern/Afro-Am), a Quaker (Asian History) and Jewish (Military History/Cold War)

Personally I tend towards agnostic theism.

With the same disclaimer made by other posters re sourcing, my perception is that academic historians as a group tend to be less religious than the general population and more religious than academics in general.

As others have written, there are specific areas related to religious history that seem to be dominated by religious people, for obvious reasons.

In my experience at university in Poland history attracted a bit more religious people than international relations (I have studied at both faculties, of course it is strictly anecdotal though). It has less to do with religion as such than with fact that right wing views in Poland tend to correlate with more interest in both Catholicism and history of Poland. So more people with that kind of background decided to study history and later specialise in Polish history rather than world history. People with more liberal views often were more attracted to specialisations in other cultures. It is of course broad generalisation and I do know some deeply devout Catholics passionate about studies of Asia and atheists specialising in national history issues.