I think you should look to Co Cavan. My gggrandfather was Simon Farrelly from Crossbane, Mullagh parish, Co Cavan. He was born around 1829 in Crossbane and his father was Conor Farrelly. Records show that Conor's father was Patrick, his mother Mary, and he had siblings Michael, Rose, Mary, Ann, Ellen, and Bridget. The 1821 census for Mullagh lists a Nicholas Farrelly, wife Elinor, and son Laurence, age 1. This information came from correspondence between Sheila Farley Comerford and Concepta McGovern of the Cavan Geneaological Research Centre. Sheila's gggrandfather was Edward Farrelly and he lived next door to my Simon in Manhattan in 1885. Did your Nicholas live in NYC?