This song is one of those that I can't seem to get any definitive information on. Every time I find it, it's under a different title, or a different artist. I have found it, variously, as "The Ball of Kerrymuir," "Four and Twenty Virgins," "The Ball of Ballyknure," and "Gathering of the Clans." I have seen it listed as Traditional, and by various artists, even Jim Croce! (On his "Jim Croce Live: The Final Tour" album)
Suffice to say, one thing holds true through every incarnation: it's probably the bawdiest of the filk/folk genre, and is certainly not appropriate for younger listeners.
The version I have here is the most complete I've seen, and also appears to be more traditional, due to the spelling and grammar.
This can be sung in many different ways - this arrangement is by no means intended to be definitive.