I would be highly interested in finding data on county level for the Kingdom of Hungary in 1910. (though of course data on even smaller administrative structures like municipalities would be amazing as well)
Till now I found this on Wikipedia https://en.wikipedia.org/wiki/Demographics_of_the_Kingdom_of_Hungary_by_county#Bjelovar-Kri%C5%BEevciThough it is incomplete.
So while I continue searching myself I thought it might be smart to ask here in the meantime if anyone knows a good place to find that data. (Best would of course be data that is freely accessible)
Do you know hungarian? If you are, you are in luck, this webpage has all the scans of the original publications related to 1910 census in Hungary. The first link (publication dated 1912) is the most comprehensive one, and offers all of the data with intorductory summaries (in hungarian and french) but also all the collected data on county as well as village/municipial level.
However to navigate it you should probably command a decent grasp of Hungarian, or at least arm yourself with google translate and lots of patience.
Also this old thread has some other suggestions which may or may not be of help