Wikipedia
McNulty (MacNulty) is an Irish surname historically associated with County Donegal in northwest Ireland and, possibly, with the moniker Ultach, an agnomen used by some of MacDonlevy dynasty in its earlier Gaelic language form. The surname denotes that its bearer comes from the Irish over-kingdom of Ulaid (Ulaidh in modern Irish, the singular being Uladh, known as Ulster in English). It is pronounced in Gaelic language "Ully" and has been corrupted in English to "ulty".
The surname is derived from an anglicized contraction of the original Irish patronymic Mac (descended) an Ultaigh or confusion of the Irish "Mac an Ultaigh" (male) and "Nic an Ultaigh" (female) surname. Variant spellings include McNaulty, its variations McNalty and, rarely, O'Nalty, Nolty, McNult, the more primitive Anglicizations McAnulty, McEnulty and McKnulty and others.
In County Clare and its adjacent County Tipperary in the southwest of the Republic of Ireland, the toponymics Connoulty and Kinoulty are encountered. Clonoulty (Irish language "Cluain Ultaigh", meaning "the meadow of the Ulsterman" or Ultaigh) is a civil parish in south County Tipperary. Some sources consider the surnames Connoulty and Kinoulty to be variant Anglicizations of the Irish language Mac and Nic an Ultaigh surname.
The surname McNulty and any of its variations may be encountered sans their mac or mc prefix. Accordingly, some persons of this surname and their namesakes may be found alphabeted instead of at "M" at "N", "O" and even "U". Capitalization and spacing are inconsistent following either prefix. Mac appears in anglicized contraction not only as Mc (also written M), but, even, M'.