American Monarchies:

There've been plenty of dictatorships in the Americas, and plenty of places ruled by European monarchs. What, however, was the last North or South American state (and not merely a tribe or collection of tribes) that was ruled by a locally resident monarch?

I have a guess as to the answer in the comments, but I'm not positive that I'm right.

UPDATE: Whoops, at first omitted the italicized "locally resident." I am not looking for the "plenty of places ruled by European monarchs" (in the sense of those who live in Europe) but rather for an American country ruled by a monarch who sits within that country (regardless of where he was born).