Ryan is amongst the ten most numerous surnames in Ireland with an estimated population of twenty-seven thousand five hundred. Only a very small proportion of these use the prefix O. Subject to one exception, to be noticed later in this section, it is safe to say that the great majority of the 27,500 Ryans are really O'Mulryans this earlier form of the name is, however, now almost obsolete: even in the census of 1659 in County Limerick, Ryan outnumbers Mulryan by about four to one, and today there is not one O'Mulryan or Mulryan in the telephone directory.
The Sept of Maoilriain was located in Owney, formerly called Owney O'Mulryan, which forms two modern baronies on the borders of Limerick and Tipperary, in which counties the Ryans are particularly numerous today. They do not appear in the records of this territory (formerly belonging to the O'Heffernans until the fourteenth century, but after they settled there, they became very powerful. Nevertheless they did not produce any really outstanding figures in Irish history or literature, except the romantic character known as Eamonn a 'chnuic, or Ned of the Hill, i.e. Edmund O'Ryan (ca.1680-1724), Gaelic poet, gentleman, soldier and finally rapparee, beloved of the people, though he met his death through the treachery of one of them. Two abbs called O'Ryan were executed during the French Revolution. Luke Ryan (ca.1750-1789) first an officer in the Irish Brigade, made a huge fortune as a privateer, was condemned to death and four time reprieved and having been cheated out of his money, died in a debtor's prison.
Many Ryans have distinguished themselves in the United States. Father Abram Joseph Ryan (1838-1886), of a Clonmel family, was poet of the Confederates in the Civil War; another Tipperary man, Patrick John Ryan (1831-1911) was Archbishop of Philadelphia; and Stephen Vincent Ryan (1826-1896) from Clare, was Bishop of Buffalo. In other walks of life the most note-worthy Irish-American of this name was Thomas Fortune Ryan (1851-1928), a millionaire who began life as a penniless youth.
The Ryans of County Carlow and other counties in that part of Leinster, are distinct from those dealt with above, though both are of the race of Cathaoir Mr, King of Leinster in the second century. These are the Riain, not Maoilriain: the chief of this Sept was Lord of Ui Drone (whence came the name of the barony of Idrone in County Carlow).
From The Septs of Ireland - Heraldic Artists,