Today, Bohemia is a region in the Czech Republic. Historically, Bohemia was a feudal fiefdom that eventually got incorporated into the Austro-Hungarian Empire until the Empire's collapse in WW1 when Czechoslovakia got it's independence. Bohemian as a nationality would probably appear in some old records as that is what people from that area were once called. Today they are no longer called that since today it's part of the Czech Republic. They would be called Czechs today and Czech people refer to people earlier in their history as also being Czech, even though at the time that's not what they were called.