The song is from North County Wexford. The Barony of Bantry, in the County of Wexford was in place as far back as 1672.
Moneyhore is a townland in the Barony of Bantry and was the home of Thomas Cloney, one of the leaders of the 1798 rebellion.
Lewis's Topographical Dictionary of Ireland, 1837 identifies Moneyhore as a place where cattle fairs 'are held at Moneyhore on the 25th of Feb., March, and May, on Oct. 2nd, and Dec. 7th; four of these are held by patent, for which a fee of 15s. per ann. is paid to the Crown by Mr. Wm. Condon, of Dublin.' Faction fighting and at least one death, are reported as occurring at the fairs.
The first printed version of the song is in a readily available book by Patrick Kennedy titled 'The Banks of the Boro : a chronicle of the County of Wexford'. According to the author, the book relates events that took place in 1817/18. One of the characters in the book sings the song. The manuscript of the book, again according to the author's preface, was completed in 1856. The book appears to have been published in 1869.
The words of the song have been altered a little along the way. This includes the modernisation of archaic words such as 'pathriarchs ' and 'bekase'. (Personally, I prefer to sing the song in as original a version as is available, and I like the selling of the corn and the washing of the sheep).
I agree with Dave Rowlands, who is a considerable expert in military history, about the origins of the song being in the Carlist war period (see above). This is obviously after the 1817/18 period that Kennedy states he is relating. More likely, Kennedy heard the song, or possibly even wrote the song, much closer to 1856 when he claims to have completed the manuscript. The 'dirty King of Spain' is a fairly clear reference to the 'Carlist pretender' to the throne, as opposed to the Spanish Queen.