Vikings were in Kilkenny, but the story is hard to get. The Vikings were in Ireland from about 800 to about 1000
Vikings founded Waterford, not thirty miles down the river Nore.
Kilkenny existed then as a monastic settlement. Monastic settlements were prized raiding properties; this is true not only for the Vikings but for rival clans.
You could take a boat up the river Nore, as long as you waited until it rains. None of those fancy Viking keels, either. You'd never make it.
In 928, Vikings committed a slaughter at Dunmore Cave, just outside of present-day Kilkenny City.