There are lots of academic studies that show that the Southern accent and vernacular is not dying out but we might as well start with the Wikipedia article on the subject.
“The Southern U.S. dialects make up the largest accent group in the United States,[10] from the southern extremities of Ohio, Indiana, Maryland, and Delaware, as well as most of West Virginia and Kentucky to the Gulf Coast, and from the southern Atlantic coast extending to most of Texas and Oklahoma, and the far eastern section of New Mexico. Southern American English can be divided into several regional dialects and sub-dialects. African American Vernacular English (AAVE) has common points with the Southern dialects due to the strong historical ties of African Americans to the region.”
The really odd thing is that some areas that speak with a mostly Southern accent aren’t even traditionally thought of as Southern at all. I can attest to that. I used to work on the Ohio/Indiana border (Richmond, IN area) and the people that are from there generally speak with a pronounced Southern accent as well. It really through me off until I looked that a dialectic maps that show some strange protrusions of the general accent that extend well outside the South including parts of solidly Midwestern states like Illinois, Ohio and Indiana but also well into the Mid-Atlantic region in parts of Delaware.