Dear DebbieH:
Many thanks for your query to the Ireland Reaching Out message board and welcome to the site.
I have found a civil birth entry for Patrick McMahon in the Irish Genealogy Civil Registration Records. They are available for free on the website:
https://civilrecords.irishgenealogy.ie/churchrecords/civil-search.jsp
You should note that the Civil Registration District is Castleblayney and this is important if you are looking for other births, marriages or deaths for this family.
I have also found Patrick and his parents in the 1901 Census and you can follow this link here:
http://www.census.nationalarchives.ie/pages/1901/Monaghan/Broomfield/Drumavaddy/1628849/
I believe that Patrick was also in Monaghan in the 1911 Census. Here is the link for that entry:
http://www.census.nationalarchives.ie/pages/1911/Monaghan/Broomfield/Drumavaddy/801909/
From the 1911 Census, it would appear that Patrick's father, Francis died between Censuses.
I have a civil death record for him having died on 2 February 1904 and I have attached it for your reference. He is the first entry on the page.
McMahon is not a common Monaghan name. I know this from my husband's family as they also had a McMahon from Monaghan who married his aunt.
If you need any further assistance, please let me know.
The best of luck with your research and thanks for your interest in Ireland Reaching Out. Please consider creating a profile for any of your ancestors under the XO Chronicles tab at the top of this page. It may assist you with finding others who are researching the same family.
Kind regards,
Jane.