This is a long shot, but on the off chance -
Perhaps this fellow fibbed and said he was Protestant, in the hopes of getting a more merciful sentence? You might even want to try searching the Catholic records.
On the possibility that this guy was really descended from a C of I line, I took a look at the religious census of 1766 in the hopes his father's family might be in there:http://search.ancestry.co.uk/search/DB.aspx?dbid=5990
but I don't find anybody named McCarthy in Cork or in all of Ireland for that matter.
Even as recently as the 1901 census, there were very few McCarthys in Ireland who were tallied as members of the C of I. Another long shot - but the townlands and streets in Cork City listed here might be places to focus on, and from there figuring out what church parishes to search.http://www.census.nationalarchives.ie/search/results.jsp?cen...