In my post above, I distinguish between the deep South and the upper South.
The deep South is traditionally the states the formed the Confederacy before Lincoln started assembling forces to force them back into the Union by force. These were South Carolina, Georgia, Florida, Alabama, Mississippi, Louisiana, and Texas. They also had the largest slave populations in percentage terms. The other slave states joined later/ were deeply divided about the whole thing.
These states except for Texas and Florida are still a good definition of the deep South. After World War 2, Florida experienced lots of population growth due to migration from the Northeast and Midwest, also immigration from Puerto Rico and outside the US, mainly in areas that had been lightly populated beforehand. Only the northern quarter of the state remains in the Deep South. Texas has always been its own region, and had a post-World War 2 settlement pattern similar to Georgia.
The interesting thing is that except for the Presidents from Texas, Jimmy Carter is the only President of the US either born in or elected from one of the deep South states. In fact, he is the only Democratic, Republican, or Whig nominee who fits that description. Two Presidents were born in Texas and three had held elected office in Texas. From the rest, nothing. This extends even before the Civil War when the typical President was a slaveholder, though from the Upper South.
Washington, Jefferson, Madison, Monroe, Jackson, Polk, Taylor, Truman (very technically) and Clinton all from the Upper South. Lincoln and Wilson born in the Upper South. The Bushes, Lyndon Johnson, and Eisenhower all elected from or born in Texas. But only Carter from the deep South.
The Upper Midwest, the Mountain West, and the Pacific Northwest also have put no-one in the White House, but they were all settled later. South Carolina and Georgia were two of the thirteen colonies.