All interesting…..but as I expect you realize, the importance of “church attendance” varies. Christians somewhat universally are expected to have a church and be there most or all Sundays. Muslims do not feel the same kind of pressure to attend services on any sort of regular basis, or even belong to a mosque.
So, for nonChristian religions…..I expect that “religious identification of the local population” is a better metric than “religious attendance of the local population.”
BTW, curious. There is a big dark dot somewhere in around Wyoming/Colorado area of Eastern ORthodox members. Is that Denver? Datawrapper isn’t giving the location on the flyover.