"Killahy", or Killaghy, a parish, in the barony of Cranagh, county of Kilkenny, and province of Leinster, 3 miles (S. W.) from Freshford: the population is included in the return for Tullaroan. This parish comprises 1564 statute acres: it is a rectory, in the diocese of Ossory, entirely impropriate in J. Butler Stopford, Esq. An abbey is supposed to have been founded here in 548. Near the old church are some remains of the house or castle of Killaghy, belonging to a branch of the Grace family. [In the R. C. divisions it forms part of the union or district of Urlingford.] school.
[From A Topographical Dictionary of Ireland (1837)]
Note: There is another Killahy parish in the barony of Knocktopher, next to the civil parish of Kilbeacon, and in the R.C. parish of Mullinavat (formerly part of Kilmacow R.C. parish).