Answer: Absolutely nothing!
Before I can figure out any pertinent genealogical gems like why those Townsend families chose to move, nearly en masse, from South Carolina to Florida, it would help to get a grasp of what life was like before 1850 in Marlboro County.
I take my tip regarding Marlboro County from the headstone of one of those many senior Townsend folks buried in Madison County, Allen Townsend. According to his headstone, he was born in 1801 in Marlboro County, South Carolina.
Of course, you and I know that it is quite possible that two people living in the same town and claiming the same surname might not be related at all. However, despite lacking any tangible record of relationship between my third great-grandmother, Delaney Townsend Charles, and this other Townsend man, I do have a reason for pursuing this lead. An irritating reason: Marlboro County—and one Townsend couple in particular—are plastered on every Townsend DNA-match's tree I've encountered, asserted to be the parents of Delaney Townsend Charles.
Without documentary support. Hence, the irritation.
Since I can't find any paper trail to lead me in a different direction, I decided I may as well follow the trail and learn what I can about the Townsend digs in Marlboro County. In the meantime, prepare to formulate a research hypothesis and test it to see if it holds up to scrutiny. After all, I can give it my best go to prove wrong the contention that Delaney Townsend's parents were John and Kiziah Townsend of Marlboro County.
Checking out the usual sources for research overviews, I learned that Marlboro County was established in 1785, making it quite reasonable to expect access to land records by 1786, and—more to our point—probate records by 1787. The difficulty with losing Delaney before 1860—the date and place of her death has yet to be documented—is that I have nothing beyond her 1841 marriage record and the entry of her family in the 1850 census to trace her adulthood in Florida. What brought this young, unmarried woman to Florida from South Carolina is, so far, unclear.
There was, by contrast, information abounding for Delaney's supposed parents, easily accessible through other posted family trees. From a typewritten listing of burials in Marlboro County, including several Townsends, I could see that John and Kiziah were buried there at Mossy Bay Cemetery. This, of course, led me to the Find A Grave entry for the same location.
Based on the information etched in the headstones, we can see that John Townsend died in 1843, not quite supporting the scenario of a fatherless child being quickly married away in 1841. The key, one would suppose, could be found in reading John Townsend's will, which hopefully would be careful to actually name his descendants. That, however, is easier said than done, as the digitized court records are available, browse only, at FamilySearch.org. And though some are searchable in a record set at Ancestry.com, a search for all Townsend documents in Marlboro County comes up short for the right John.
The curious quirk is that, if the record were readily available to access, why hasn't anyone footnoted as support of Delaney's position in that family that she was mentioned in such a document? Perhaps she wasn't. Perhaps this was not her father. But to demonstrate that, we'd first have to locate such a will.
Meanwhile, as I'm "browsing" through such a resource, there are other resources I've discovered—and more to share, while I'm sparing you the sausage-making tedium of grinding through microfilm records.