http://www.tennessee.gov/TSLA/histor...historians.htm
Each county in tennessee has a local historian. These people usually have access to maps, deeds, and other documents that have been archived by the state. They may have your answer.
My personal feeling about the courthouse layouts is the fact that in the early days most people would come to town in wagons to do their business. I think the layouts may have been created to facilitate the hitching of teams and allowing an easy way for the horses to circle the square without trying to backup and etc. Just a thought.
Kerry