Goofy as it may sound, this is really the only acceptable way of referring to a person who hails from the USA's fine State of Michigan.
Using the word "Michiganian" in its stead is clearly "just plain wrong".
Oddly enough, probably due to the cosmic influence of the geekly mecca that is Holland, MI, there are quite a few past and present Michiganders among your fellow noders, including nate & dem bones, CmdrTaco & Hemos, thefez, Saige, kaytay, sabby, Void_Ptr and... oh yeah, me! (See the Registry for the current roster.)
In general, Michiganders tend to be industrious, slightly overweight, obsessive about their automobiles, apathetic towards the weather, and masochistically supportive of their local sports teams. Michiganders from the state's colder Upper Peninsula ("yoopers") like to make fun of Michiganders from the more-populous Lower Peninsula ("trolls"), and vice versa.
See also: You Might Be A Michigander If...