Sorry I spelt Scanlan's name wrongly in the quotation above. When I looked again at the article, it is "William J Scanlan" and there's quite a lot of info about him at the "Composers-Lyricists Database" at
http://nfo.net/cal/ts1.html

He was born in 1856 at Springfield MA and among the list of songs he composed were "Over the Mountain" and "Moonlight at Killarney".

So it does look as if "Where My Eileen is Waiting" has an Irish-American origin! Unless anyone knows anything to the contrary.