mee

When I was child I remember my mum saying the reason Kilkenny was a city was because it had:
1) Two cathedrals Anglican and Catholic. Given Ireland was mainly by England for many centuries it would make sense that the Church of Ireland had to have a presense in the form of a Bishop in any city.
2)Royal Charter
3) Certain threshold in popultion

In any event since Kilkenny was once the capital of Ireland it is only fair that it should be rewarded with city status.