Not sure if this is of any help to you or not.
My great grandmother was Mary Clancy McKiernan. She was married to Bryan McKiernan. They lived in the district of Manorhamilton, Drumkeeran, on the townland of Mullaghbaun. They can be found in Griffith's Valuation. According to a copy of Mary's death records, she died at the age of 63, therefore she was born 1821. (Bryan b. 1814, based on his death record.) My maternal grandfather, James, was next to the last of their children, having been born in 1865.
A few of Bryan and Mary's children married people by the name of Lyons and Gallagher - siblings marrying siblings!
Wondering if your Clancy could be related to my Great Grandmother.