The title is The Fairies.  In the DT:

King of the Faeries  An incomplete text with the wrong title, wrongly described as "traditional", and the well-known author uncredited.

In the Forum (amongst quite a few discussions):

Lyr Req: King Of The Faeries  In this thread I posted the full text of William Allingham's poem.  Bits of it are regularly posted here, so it seemed sensible to get it out of the way, and to correct the fanciful spelling; Allingham used the usual "fairies".

A band called "The Irish Rovers" (from which I assume they were American) set it to music years ago, but nobody, so far as I can remember, has ever told us what tune they used.  Some have assumed, from the new title they gave it, that it was the set-dance King of the Fairies, but there seems to be some doubt.  Does anybody actually remember?