While traveling recently, I was in Billings was discussing with a bartender about the local dialect and where various boundaries of production were and pulled up this map.

Both the pin / pen and the on / dawn / don differences between how I pronounced words and he she pronounced words were evident - it was rather interesting and being able to hear the difference.

Btw, its a bubbler. http://shop.wisconsinhistory.org/productcart/pc/Bubbler-Magn... and http://csumc.wisc.edu/wep/map.htm

While listening to A Way With Words ( https://www.waywordradio.org ) some time back I there was a woman calling in about a word (Pitch in) the caller didn't know and apparently everyone in the town knew. Turned out to be a local dialect word choice that the hosts were able to pin down to small pockets of townships in Indiana. The episode is https://www.waywordradio.org/regional-term-pitch-in/

I'll also toss in an older dialect survey with maps - http://dialect.redlog.net/maps.html