Sharon,
John O’ Reilly married Mary Cassidy on 29.5.1890. The civil marriage certificate tells us that his father was Bernard O’Reilly deceased. John was living in Knockbride townland (in the parish of the same name) at the time of his marriage.
https://civilrecords.irishgenealogy.ie/churchrecords/images/marriage_returns/marriages_1890/10699/5900309.pdf
Bernard Reilly looks to have died before 1878. There are half a dozen or more men of about the right age who died between 1864 (when death registration began) and 1877. The records for those years are not on-line free yet so you would need to pay to view them.
I looked in Griffiths Valuation for Knockbride townland in 1856 and don’t see a Bernard O’Reilly/Reilly listed there. So the family appears to have arrived after 1856. I noticed this family in Knockbride in the 1901 census, just a couple of houses away from John & Mary.
http://www.census.nationalarchives.ie/pages/1901/Cavan/Skeagh/Knockbride/1054393/
The family were Terence O’Reilly & Margaret MacIntyre or MacEntyre depending on which of their childrens birth certificate you go by. Their son Eugene was born 25.1.1886 at Knockbride which gives me the parents names. Terence died there 1.12.1897 aged 52. I haven’t been able to find their marriage so can’t tell you who Terence’s father was. It wouldn’t be surprising if Terence was related to John O’Reilly.
You can use the Valuation Revision books (held by the Valuation Office in Dublin) to find the plot numbers for each of the O’Reilly households in Knockbride. You can then use the maps on the Griffiths Valuation site to identify exactly where each one was/is.
There were about 25 farms in Knockbride in 1856, plus some labourers cottages, a school and a chapel. A total of 386 acres for the whole townland. I notice from Griffiths that a William McEntyre rented plot 1. That was a 44 acre farm. So possibly that’s where Margaret/Maggie McIntyre came from. Possibly the O’Reilly family married into the farm? I have no firm evidence for that but it wouldn’t be unusual. Plus there are no McIntyres living in Knockbride by 1901. So they had gone and someone else had acquired their farm by that year.
http://www.census.nationalarchives.ie/pages/1901/Cavan/Skeagh/Knockbride
http://www.askaboutireland.ie/griffith-valuation/index.xml?action=nameSearch
Frances McIntyre died at Knockbride on 13.8.1886 aged 60. A farmer’s widow. The informant was her daughter in law Kate McIntyre, also of Knockbride. Francis might be William’s widow. I can’t see a death for him so suspect he died before 1864 when death registration started.
https://civilrecords.irishgenealogy.ie/churchrecords/images/deaths_retu…