The O'Nuallains were princes of the Foharta, now the Barony of Forth in County Carlow, Ireland. In pre-Norman days their chiefs held high office under the Kings of Leinster. In Irish the name O'Nuallain means descendant of Nuallan; the word Nuallan means a shout or cry. The name was anglicised O'Nowlan, Nowlan, and Nolan. To this day, Nolan is among the forty most numerous names in Ireland.
Nowlan men began emigrating to the New World after the rebellion of 1641-1662 had been suppressed. They had supported the Catholic side and, as a consequence, lost most of their land, which was included in the grant made to James Butler, Earl of Ormonde, Lt. General of the Protestant forces.
John Nowlan (c.1634-?) had three sons, John, William, and James. The fate of John Jr. is not known. William emigrated to New England. James became an indentured servant and made his way to Virginia. Along the way, his name became Nowlin.
Source - History of Carlow CO, Ireland by John Ryan