some uneducated commentary

I have nothing factual to add to this conversation, all of the following is merely opinion and conjecture

(1) The scene of the song appears to be a place where conscription is not in place.
(2) The writer may well be more eduacted than the broader audience it was written for
(3) Much harvest migration between the North of Ireland and Scotland would have given shared lingo, Even Donegal Irish dialect is quite a bit different to the rest of the country. Come to think of it the textbook crap now taught is more like English every year.
(4) It may well have been written in England or Scotland by an Irish immigrant and even if so; who knows what they thought of their primary nationality after migration (if its written by an Irish man while in Scotland, is it an Irish song or a Scottish song?...very subjective and i dont think we will ever know. though seems more logical (to me)to think it was written in an area where conscription did not occur & for this reason, I feel Donegal or Scotland (migrant entertainment) are the most likely origin.
(5) my perception of this is that it is not an anti war song, if written (or set) in Ireland, it would be more an affront to the arrogance of British recruiting Irish under the carrot and stick of pay lure and economic suppression. The distain for the uniform would suggest to me a nationalistic element to the affront rather than just the socialist element of the military taking advantage of the poor.
The author may well not have been anti war or anti recruitment...if it was for the right cause; either a social cause or a national one.
(6) Harvest migration may also explain how the song may have travelled quickly across the isles.

My conclusions are that it is likely written by an Irish person or by an artist appealing to that community, the location of its writing being the least important element to understanding the meaning of the the original author.

I have thoroughly enjoyed the reading in this thread and thank all the contributers. It has added an extra level of romanticism to the song with the mystery surrounding its origins, and may do the song better service to remain that way. I am delighted to have learned through all the links you have given that the lyrics by and large are completely unchanged over nearly two centuries. Which makes this song even more of an absolute gem.

before I die i would dearly love to be able to play the guitar like Paul Brady, and the outstanding tone in his voice early in his career, He cannot even match the beauty of his late 70's recording himself later on, let alone anyone else do a better job. And he makes the entire playing and singing look so unbelievably effortless. the song the man and the age he did it at are a match made in heaven that i cannot ever see being bettered. But beauty is in the ear of the beholder, so I'm not asking anyone to agree with me.