McNulty (Irish: Mac an Ultaigh)—also spelled MacNulty, McAnulty, McEnulty and Nulty amongst other variations—is an Irish surname, meaning "son of the Ulsterman". Usually considered a branch of the Ulaid ruling dynasty of Mac Duinnshléibhe (MacDonlevy) who fled Ulaid to Ailech after the formers conquest in 1177 by the Normans, DNA analysis points to descent from other Ulaid families as well. After the Battle of Kinsale in 1602, some McDonlevys and McNultys migrated to the province of Connacht where their name is now common.
The name is said to have arisen from a branch of the ruling Ulaid dynasty of Mac Duinnshléibhe (MacDonlevy) who had migrated to what is now County Donegal in the Republic of Ireland after John de Courcy's conquest of Ulaid in 1177. Here some of the MacDonlevys were nicknamed Ultagh/Ultach. However, historical records such as the 1659 "Census" as well as Griffith's Valuation (1848-1864) show that concentrations of McNultys were found in parts of Ireland where the MacDonlevys had little presence, coupled with DNA analysis showing that the McNultys may actually derive from other Gaelic families that migrated from Ulaid and not just the MacDonlevy's. The names Ultagh/Ultach and Mac an Ultaigh applied to only those that fled Ulaid and was not used for those that remained.
Regardless of their actual origin, the first McNulty to be recorded is found in the Annals of the Four Masters under the year 1281, where an "Murtough Macan-Ulty" is listed as a distinguished fatality at the battle of Desertcreagh in present-day County Tyrone, Northern Ireland.
The probable transition of the name Mac an Ultaigh from the Ultagh MacDonlevy's can be seen around 1601 where one "Morris Ultagh" is recorded as "Morris m'Nich Ultagh". The surname prefix "m'Nich" appears to be an English confusion of the female prefix Nic with the male prefix Mac.
In County Clare and its adjacent County Tipperary in the southwest of the Republic of Ireland, the toponymics Connoulty and Kinoulty are encountered, and are believed to be Anglicisations of Mac an Ultaigh.
By 1980, there were 19,469 persons surnamed McNulty in the United States Social Security Administration data base. The surname McNulty was, then, the 2332 most frequently occurring surname in that database. Some of the first McNulty immigrants to North America arrived in Philadelphia and New York City in the very early 19th century and, later, more numerously, in both Philadelphia and New York City between 1840 and 1860, during which period the great Irish Potato Famine occurred.