I got the following from About.com.
Ireland was one of the first countries to adopt hereditary surnames, many of which were devised during the reign of Brian Boru, the High King of Ireland, who fell defending Ireland from the Vikings at the Battle of Clontarf in 1014AD. Many of these names began as patronyms to define a son from his father or grandson from his grandfather. Thus, the reason for the common prefixes found on Irish surnames. Mac, sometimes written Mc, is the Gaelic word for "son" and was attached to the father's name or trade. O is a word all by itself, signifying "grandson" when attached to a grandfather's name or trade. The apostrophe that usually follows the O actually comes from a misunderstanding by English-speaking clerks in Elizabethan time, who interpreted it as a form of the word "of." Another common Irish prefix, Fritz, derives from the French word fils, also meaning "son."
Does your family carry one of these 50 common Irish surnames.
YES! In Ireland, whose population is about 1.36% of that of the US, Doyle is in the list of 50 most common surnames. (In the US, it's the 419th most common last name, according to the US Census Bureau.)
The name comes from dubh ghall, the "dark foreigner," and is thought to be Norse in origin. In the province of Ulster they were known as Mac Dubghaill (MacDowell and MacDuggall). The greatest concentration of Doyles is in Leinster, Roscommon, Wexford and Wicklow.
And I didn't even make an effort to wear green today.