I always thought "Muirshin Durkin" referred to the town the man of the song was leaving. The place-name "Deargain" Anglicised as Durkin occurs in Co. Kerry.

And yes, Ewan Macoll wrote "Dirty Old Town" about Salford, near Manchester, England, but before the days of the radio ballads. Not every song you hear sung by Irish groups is an Irish song. I've even heard Macoll's "Shoals of Herring" - about the Norfolk fishing industry - turned into "The Shores of Erin"!!!

That's the folk process!!!