So this is still a WIP, but it's coming along nicely. This is the ethnic majority map. The % of the majority ethnicity are shown for each political district (okres). Bohemia and Moravia-Silesia were further subdivided into judicial districts but I decided not to show that for the sake of showing everything at the same level. The data is from the 1931 census, which is really thorough.
For reference, Czechoslovaks are in red, Germans in yellow, Hungarians in green, Rusyns (Ukrainians and Russians too) in purple, Poles in dark blue and 'Jewish' (as ethnicity, not religion) in teal. The 1931 census derived ethnicity from self-identification. As a results, some numbers may be suspect especially where Poles lived or in urban Slovakia. Many Jews in Bohemia and Moravia identified either as German or Czechoslovak.
A religious map will follow soon after I finish tracing all the districts. The more interesting numbers will be those of the Czechoslovak Church, a modernist Catholic splinter that became a sort of hyper-influential national church in Bohemia (especially) and Moravia. It claimed to be neo-Hussite and combined elements from modernist Catholicism, Protestantism (Hussite and otherwise) and elements of Orthodoxy. Masaryk was a member.