Following up on GeoffLawes's post above (2004):

An ad in The Era (London), Oct. 16, 1859, touts "Mr. H. R. Clifton, Comic Vocalist," who had been appearing regularly for many months at Jude's in Dublin.

Among songs mentioned as being in Clifton's repertoire was "The Rocky Road to Dublin," written not by him but by the lyricist "Harry Sydney."

That the Sydney song was soon known in the United States too is shown by its offhand mention, as something familiar, in the Buffalo (N.Y.) Commercial (Aug. 31, 1863).

The earliest mention of the tune in America may be that in the Portland (Me.) Advertiser, March 22, 1853. By 1856 it was alluded to in the Trinity Journal (Weaverville, Calif., Apr. 19).

The Traditional Tune Archive shows that no fewer than *eight* other, unrelated U.S. fiddle tunes have more recently gone by the Irish title.