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Are you aware of any sibling to Catherine? I searched the subscription site Roots Ireland and the 1833 Catherine Donoghue in Killarney with parents John Donoghue and Catherine Cournane had three siblings: Ellen 1829 John 1836 Elizabeth 1840t Ages provided on death records are not always accurate since many immigrants made themselves younger or older in their new country. Ages in general were less exact in the 19th century.
The townland for the family above would be Coolies in Killarney civil parish.