Found some interesting info and site that may be useful to you and anyone else researching Irish lines.
This site seems to combine & confirm all the info I found, with that supplied by you, Hughie and
Sweet Caroline yesterday.
If I have my geography correct, I think counties Armagh & Louth border each other ? If that is the case
then there is a good chance that the following info may be relevant to you ?
Nevertheless, if not, It seems a good site for Irish research and full of GOOD information.
On Google, type in: http://www.censusfinder.com/ireland.htm
scroll down to the county Armagh section then click onto:
1901 County Armagh Census Strays.
At the top of the page there is some census info on a Donnelly family that may or may not be related
to you. At the bottom of the page there is some info that mentions county Louth. Again, this may or
may not be useful to you ? It was all gobbledegook to me but maybe you can make more sense of it ?