Accents are likely a result of generations of people living in a certain region, developing 'localisms' in words and pronunciation. I've read that American regional accents have diminished as people are more mobile, I certainly see it of people my generation that have moved around a lot..
My parents were from rural Kentucky, but spent most of their adult lives in various parts of Ohio and S. Florida..growing up w/ them in E. Ohio, I didn't really notice any accent--compared to my cousins, aunts, uncles and grandparents that lived in various parts of Kentucky and S. Indiana. I did notice distinct accents from people in my area from the West Virginia panhandle (just across the Ohio River) and from nearby Pittsburgh.
I spent my jr high and high school years in the Florida Keys, around a lot of different accents because so many people weren't from there...then as an adult, I've lived in NE Ohio, SE Michigan, Colorado and Arizona..
People think I'm from California, I guess because I have a neutral accent--kind of a typical American TV newscaster accent.
I worked with a lot of Canadian transplants in Colorado, and several words always stood out for me--about, out, process, and Java (the computer language)...plus their generally higher alcohol tolerance.