This is the closest thing to a study on religion in prison I’ve ever found and the prisoner statistics are obscured by whether chaplains considered them extremist - the clearest piece of data is that 44% of chaplains (a plurality of them) are evangelicals. It’s a really shaky statistic though so I wouldn’t draw on it outside of dunking on idiocy from the GOP

Study: https://www.pewresearch.org/religion/2012/03/22/prison-chaplains-exec/