KELLY is of Irish origin, and is the second most common name in Ireland, and the 69th most popular name in the United States. There are various origins.
It is an Anglicized form of the patronymic Gaelic name O’Ceallaigh, meaning "descendant of Ceallach," from the Gaelic prefix “O” meaning "descendant of" and the ancient Irish personal name, Ceallach .
Originally a byname meaning ‘"right-headed," it was later understood as "frequenting churches" from the Irish ceall. Several early Irish saints bore the name.
It may also be of English origin, from a place in Devonshire recorded as “Kelli” in the 1194 Pipe Rolls. It may also be of Scottish origin, from the lands of Kelly near Arbroath, Angus.