Looking at the National Archives census website, I read that the 1821 and 1841 census for Cavan was complete. So If I find the only Hugh Farrelly, age 19, in the 1841 census, living in Killeshandra (Townland - Kilgarve), should I assume this is my GGgrandfather. I now know that he had a a baby girl Mary born in 1853 (thank you Lesley for this info) with his wife Anne Donoho, who is also listed in the 1841 census in a Donoho household. I had first thought his first child was Julia with her birth date listed as 1861 on a US census. I think this is off by a few years because I found her brother Hugh Jr born in 1861 in church records. I now know there was maybe another girl born, Bridget, before Julia. So he probably didn't marry until the early 1850's which would put him at 28-30 years of age at in 1850 if this Hugh is my GGgrandfather.
Searching the Griffith's valuation, I came across two Hugh Farrelly names dating aound 1857. One is listed in a townland called Snakeil/Snakeel. This townland isn't listed on the 1841 census. So by 1857, my GGgrandfather is either the Hugh living on Main Street in Arvagh, (Drumalt) or he farming in Snakeil.
The church records for his children Hugh, Anne, Rose, Elisha and Ellen are in the Kilmore parish records. these records start at 1859 so I coiln't find Hugh & Anne's marriage or Mary, Bridget and Julia's births.