Hugh Quinn, Mucknaugh married to Ellen Devit

The online parish records for Mucknagh (current spelling) only go back to 1826 for baptisms, so you won't find Hugh there, but you could search the likely mid-century years for James's baptism.  Mucknagh is in Killoe parish, and the records are available at this link:

https://registers.nli.ie/parishes/0172

This link has more info about the townland of Mucknagh:

https://www.townlands.ie/longford/longford/killoe/cloonee/mucknagh/

In Griffith's Valuation (mid-1800's), there are both a Hugh Quinn and a James Quinn listed in Mucknagh (that James might have been Hugh's brother or cousin, or perhaps even Hugh's father,  since your James would presumably have been too young to hold a tenancy then).  See this link for the records:

https://www.askaboutireland.ie/griffith-valuation/index.xml?action=doNa…

In the 1901 census, there's a Patrick Quinn living with his family in Mucknagh, plus a Thomas Quinn listed separately (no doubt related) .  Patrick may have been a sibling of your James, and may have been the eldest, if he inherited the tenancy (or the land itself by then).  See the records here:

http://www.census.nationalarchives.ie/search/results.jsp?census_year=19…

I'm adding to my post to mention another research possibility.  As you may know already, the censuses earlier than 1901 are missing for most places, having been destroyed in a fire, but if Patrick Quinn lived long enough to claim a pension (they started in 1909), he may have used an old (not yet destroyed) census record (usually from 1841 or 1851) to prove his age, and that record might show your James, and his father Hugh (the pension records were not destroyed in the fire).  That was a common way for people to establish their age for pension purposes in the early years, and the records for most counties are available for free at the FamilySearch site:  https://www.familysearch.org/en/

Stievie B.:

The townland is Mucknagh in Killoe civil parish Co. Longford. The records for Killoe RC parish start in 1826 yet when I search the subscription site Roots Ireland, I can't find any baptismal records for children of Hugh Quinn and Ellen Devit.

I did find Hugh Quinn in Mucknagh in the 1853 Griffiths Evaluation head of household listing for Killoe civil parish. I also found an 1832 Tithe record showing a wheelwright named Hugh Quinn in Mucknagh with a small holding (less than an acre). http://titheapplotmentbooks.nationalarchives.ie/reels/tab//004625676/004625676_00345.pdf

So I'm very surprised that I can't locate any baptismal records.

Roger McDonnell