Josh - If you're committed to being literal (not always a good idea in folk songs), what about the next lines?

"I would swim over the deepest ocean
Only for nights in Ballygrant."

Not, you'll notice, "only for nights in Carrickfergus." In this song, "nights in Ballygrant" carries romantic implications, whereas nothing so desirable is implied in Carrickfergus. Is the singer complaining repeatedly about "nights in Ballygrant" because of discomfort? Insomnia? Bedbugs, perhaps? ;-)

Or is he somewhere in Ireland, wishing to be at the port of Carrickfergus where he can find "a handsome boatman" to ferry him over to Ballygrant? To me, that seems more likely.

Then faraway "Kilkenny" crashes into the song, unexplained and unexplainable except for its black marble, almost like a TV commercial - "and now, a message from our sponsor, Kilkenny Quarries Ltd."

But in fact, black marble is found in many places in Ireland and throughout the British Isles, including Ballygrant in Kilmeny Parish, Islay. Use Google Earth to see for yourself; from the air, the huge quarry is a dominant feature on the southwest side of Ballygrant village.

What we know for certain:
- Ballygrant, Islay, is across the Irish Sea from Carrickfergus
- Ballygrant is in Kilmeny Parish
- marble was quarried in Ballygrant
- silver was mined in Ballygrant
- Kilmeny churchyard has black marble stones
- Kilkenny is 160 miles from Carrickfergus, 220 miles from Ballygrant
- Kilmeny is 10 minutes' stroll from Ballygrant
- a lover who died in Ballygrant would likely be buried in Kilmeny churchyard

Of course, no one can absolutely prove anything about a traditional song, nor can one count on literal interpretation. Without a known and copyrighted source, traditional songs are open to every singer's personal interpretation. So if you think nights in Ballygrant are intolerable, and the leap to distant Kilkenny logical, by all means feel free to sing 'Carrickfergus' that way.