Today's Irish Central has an article on the Top 100 Irish Last Names Explained. My Irish Creedon surname is not that common, so I wasn't surprised that it didn't make the list. The explanations are short, but might provide a bit of info when you run across a new name.
The MacCarthy name is associated with some of the same areas as the Creedon name. That name is much more common, so it did make the list:
"MacCarthy - Mac Ćarthaigh (cárthach, loving). The chief family of the Eoghanacht and one of the leading septs of Munster, prominent in the history of Ireland from the earliest times to the present. MacCarthy is the most numerous Mac name in Ireland."
The full article is here: The Top 100 Irish Last Names Explained. If you click on the Print button to the right of the article title, you can bring the entire article up on one page.