Because much of my life has been spent in and around the military, I've come in contact with just about every accent you can imagine. My dad and his elder siblings still have a French-Canadian (Quebecoise, don't feel like looking up the accents) accent. Mom somehow laundered her New England accent during those years, but when she is around her family she starts to Pahk the Cah in Havaad.
I've noticed, too, that some people tend to, after a few years, start talking w/o their regional accent when face-to-face, then when you talk to them over the phone, the accent is stronger. Maybe it's just me; that I hear it more when I don't see the person talking.
When we were stateside we lived in Northern California, Nevada, Utah, Central California, and spent much time visiting family in the Mojave. To my ear, no discernable accent. My husband has traces of his Midwest origins. What I find interesting is that people from Illinois (he was born in Joliet) pronounce the first "I" as an "E" ... Ellen -noy.
The "Fargo" movie accent didn't even seem exaggerated to me. I was stationed in a very small ND town, and that's really how it sounded to me.
As I previously said, my friends when I was growing up, for some reason all had French speaking mothers; three were French, one was French-Canadian. I was out west when we were on the road, and Antoinette heard me say "kwu-bek". "Claire you know better," she sternly said, "now say that correctly." Oui Madame! Kay-bek."