In the three towns I frequent, I've seen one guy wearing his own kilt casually. He's a high school kid in our marching band (the Howell Highlanders). I also overheard someone exiting the bar as I entered exclaim to their male friend/husband/boyfriend "Hey, you should wear your kilt next time!". Totally unscientific of course, but that works out to 0.01%.

Assuming I'm off by a factor of 10, across the state of Michigan, it would be around a thousand at most. Feels like a good guestimate for frequent kilt wearers. I'm sure with the number of Scottish society members, Renaissance fair goers, etc. there are many more occasional kilt wearer/owners.

I wish I knew of a way to survey this. Someone at Facebook could probably give a good estimate based on their database.