I agree, certainly not Latin, and, in this context, not a surname, it seems. However there is an Irish surname Keady, but it's not from the town of that name. It's from the Irish Mac Céidaigh, "son of (a man named) Céadach". Céadach has been englished as Kedagh. So your ancestor may have been called Keady as a version of Kedagh, because of a connection with a Keady family, or because of a family connection with the town of Keady.