If you are a bit of a linguistics geek, then Jeff H. sent in a treat for you. He found a detailed map of accents/dialects among English speakers in the U.S.:
The creator, Rick Aschmann, is a professional linguist, though the map is described as a hobby not related to his work. It appears to be based primarily on data from the Atlas of North American English (ANAE).
A caution: Aschmann says, “I have not included AAVE [African American Vernacular English] in this study, since its geographical distribution tends to be independent of ‘white’ dialects.” That’s an important omission to keep in mind. I went to the ANAE website and also did a general search for a map of AAVE prevalence, but I haven’t been able to find one
And there is one area in the continental U.S. where the majority of people do not speak English: the parts of Arizona and New Mexico, shaded a sort of coral color, where indigenous languages are still more prevalent than English.
If you go to Aschmann’s page, you can click on sections of the map and go to a list of representative recordings of people who represent the dominant speech patterns there. You can also get a very thorough explanation of all kinds of linguistic differences that are beyond my level of interest/comprehension.