If I am not mistaken, the Farrelly and Reilly families backed up to my family's land (Mulvany) in County Cavan, Ireland. In fact, I have several members of both families married into my family tree.
My great, great grandfather was Thomas Farrelly in Kingscourt and Enniskeen, Cavan, Ireland, who was born 1843. He was named for his father, who appears in records as Thos. However, the Thomas Farrelly on my tree is married to Catherine Smith. The younger Thomas had a daughter, Elizabeth (b. Jan. 1865), and was married to my great grandpa, William Mulvany.
According to Griffith's Valuation her family leased land from my grandfather's family and farmed it, helping out on our family property as well.
If this matches up to your information, just reply and I will provide additional detail.