Would any one know where Catholics who lived in Waterford City would hae been buried in the 1870s?

I was down in Waterford with my sister last weekend from Dublin. We visited many places where our ancestors lived, but we couldn´t find their graves. The people we were researching lived in Ballybricken but later moved to areas outside the area. (Beau St and Mall Lane). We went to the graveyard of the Church of Trinity Without, but could not find their graves. (of course it is possible that their graves weren´t marked or there were some gravestones where the inscription had faded.)

Is there anywhere I could find out where these people are buried?

I would also like to say, I had never been in Waterford before, but, it is one of the most beautiful cities I have ever been in. It has not been destroyed like Dublin, where old buildings were demolished and replaced with glass monstrosities. I can´t wait to go there again.