I think you may inadvertently have linked to the entire Ballad Index, Wolfgang! This is a bit easier: Traditional Ballad Index:
Castle of Dromore, The (Caislean Droim an Oir)
This song was written by Harold Boulton, to an existing tune called My Wife is Sick (No. 509 in The Complete Collection of Irish Music, Stanford-Petrie, 1903-5). Sir Harold (1859-1935) was also responsible, amongst many other things, for the words of The Skye Boat Song and the melody nowadays used for The Lyke Wake Dirge.
Boulton's text, slightly altered, is in the DT: CASTLE OF DROMORE, and the tune is here: Mus add. Castle of Dromore (abc and miditext formats) and also at The Mudcat Midi Pages:
Castle of Dromore
The Clancy Brothers recorded the song as October Winds, again with a slightly altered text. The entry at Andrew Kuntz's The Fiddler's Companion quotes what is described as "an 18th century song" (identical but for the substitution of a pháisde bán a stór for my dearest treasure store) as Boulton's source, but unless I have missed it, gives no provenance of any kind for this earlier song, if such it be. It is perfectly possible that he may have re-worked an older lyric; this was common practice at the time. I'd be interested in any concrete information anyone might be able to add on that.
There are a number of places called Dromore or Drumore, including one in Argyll. See also this earlier discussion: Castle of Dromore.