This seems to be where it all began, in 1949. When blood tests were required for marriage licenses, Kingsland saw an opportunity. Make it easy to get a blood test and a license and reap the revenue. It was a good idea and it led to Kingsland’s distinction as the “Marriage Capital of the South”. Georgia hasn’t required blood tests for licenses since 2003, so the old sign is just a nice reminder of what helped put Kingsland on the map.
Kingsland Commercial Historic District, National Register of Historic Places
Vanishing Georgia: Photographs by Brian Brown 
I’ve heard the same tale about Folkston. I have friends who drove over the line to Folkston to get married.
It partly became the “Marriage Capital of the South” because Georgia had a lower marrying age than Florida, and Kingsland was the first town over the state line. So a lot of young couples would make the drive up so they could get married. And on an unrelated note, this is where JFK Jr. and Carolyn Bessette had their blood tests done for their secret wedding on nearby Cumberland Island.