If we go back to the colonial period then Anglicanism was very popular in the South. I dont know what percentage it was (I know the early censuses counted denomination members) but it was high. The Church of England was the state church under British rule. If I recall correctly in some colonies only Church of England preachers were permitted, though this may have been abandoned at some point prior to the revolution.
Anyway your general description seems to be accurate from my knowledge in that Episcopalian churchs are very common on the coast and and the oldest inland cities. In these areas the Episcopalian churches, which were Church of England, are typically the oldest church. Methodist churches are also fairly popular. Of course Methodism originally came from the English church, though I’m not aware of the details of its formation as an independent church. But the churches of the South reflect the early settlers in being mostly English and Scottish churches.