Fun things about the name Moriarty:
It comes from the Gaelic word Muircheartaigh (with some appropriate accents, pronounced something like Mir-art-tye) which means "the navigator" or (less likely) from The Gaelic words "Mor" ("great") and "artach"("exalted"). The name became "Murtagh" in Leinster, Murtaugh in Scotland, and Moriarty in County Kerry.
It's one of the older Gaelic names. It can be traced back at least as far as 1210 and its origin is Castlemaine on the Dingle peninsula. The Muircheartaigh clan were the rulers of west Munster in the fourteenth century.
The coat of arms is a black, double headed eagle.
Famous Moriartys include Prof. Moriarty of Sherlock Holmes fame, actors Michael and Cathy, the voice of the Gaelic League in Ireland, Michael, and some guy who flew a plane under the Eiffel Tower in 1948.
Moriarty is about the sixth most common name in County Kerry, but it is found almost exclusively there. In 1840, of the 145 families named Moriarty in the census, 142 of them lived in Kerry.