Really just the southeast. Approximately this region.
Even then it's only for the ones who act really "country." If they're from big cities or have more of a "Southern lady/gentleman" demeanor it doesn't really apply.
But yeah, AJ is explicitly given a Southern American accent in the original version. I can't tell the little differences between the accent in one southern state or another, but the wiki claims that it's most like a Missouri accent.
I know, I only watch the original version. The German translation is just plain terrible. Anyway, I wouldn't be surprised if AJ would moonshine and sell that stuff. :D