The Getty Thesaurus of Geographic Names, which is usually pretty reliable and thorough, lists nothing called Copperline or Copper Line. Several states (but not Georgia) have a creek named Morgan Creek, so that's not much help.

Google gives about 2000 hits on "Copperline". I found several copies of the lyrics, other references to the song, a couple of bands named Copperline (named after the song, I'll bet), people with the surname Copperline, and several businesses named Copperline. But not a single place called Copperline. Did JT make it up?