Hi Christine & Miriam, I have visitors currently as the Fleadh Ceoil is here in Drogheda and I am entertaining my friends of old. I have been gathering the certs for the children Miriam identifed to locate the area they lived at the time, it appears to me the graveyard is probably St Bridgids of Faughart which I think is also Kilcurry and Bridge A Crinn, a lot of graveyards are transcribed but I do not have that one, the website for there has been hijacked, Old Casltetown has been transcribed in 1922 I think so would only have Bridget if she is there, it is on your left as you go out the Castletown road from Dundalk, still in the town boundary. The library in Dundalk has the research section where these books are kept and you can email them or view the catoaogue online. The website Miriam sent has them abbreviated beside the name.
The address of Bridget McArdle is Lurgankeel or Lurgankiel, you can see the areas on this site which shows you were the townland is and it may be possible to locate the plot they lived on in the 1850s but I will return to it. There is a private Facebook page called Louth Genealogy and another mainly photos called Dundalk North End. https://www.townlands.ie
Based on the assumption Thomas would be buried with Bridget I cross referenced the deaths of them both with that name from transcribed graveyards (not all transcribed) so you can see the graveyards with the matches, you could be doing a lot of walking.
Duffy Bridget, Knockbridge, HKb / Duffy Thomas, Knockbridge, HKb
Duffy Bridget, Bridge-A-Crin Old), FHPPS / Duffy Thos., Bridge-A-Crin (Old), FHPPS
Duffy Bridget, Darver Old Graveyard, MICHDVR
Duffy Bridget Ann, Castletown, Dundalk, CGD / Duffy Thomas, Castletown, Dundalk, CGD
Duffy Bridget [McEntegart], Castletown, Dundalk, CGD assume maiden name in brackets
Duffy Bridget [McGuinness], Castletown, Dundalk, CGD assume maiden name in brackets.
Duffy Brigid, Haggardstown (Old), H&B Duffy Thomas, Haggardstown (Old), H&B
Duffy Thomas, Kilsaran, HK
Duffy Thomas, Fochart, CLAHS
Duffy Thomas, Haggardstown (Old), H&B
Duffy Thomas, Kilcurry, FHPPS
Duffy Tom Ju., Dunbin, HKb
As an aside my mothers maiden name was Thomas, assume your Thomas is not from the west of Ireland.
Regards
Pat