McLaughlin (surname)
M(a)cLaughlin is the most common Anglicized form of "Mac Lochlainn", a masculine surname of Irish origin. The feminine form of the surname is "Nic Lochlainn". The literal meaning of the name is "son of "Lochlann"". Note that "Mc" is simply a contraction of "Mac", which is also (albeit rarely) truncated to "M' ". Thus, "MacLaughlin", "McLaughlin" and "M'Laughlin" are the same Anglicism, the latter two merely contractions of the first. The original surname Mac/Nic Lochlainn was borne by a family of Cenél nEógain, a branch of the historic northern O'Neill dynasty, reputedly founded by Niall Noígíallach. This family  expanded across the North Channel into Scotland, where it became the Clan MacLachlan. M(a)cLaughlin is sometimes used as a modern form of "O'Melaghlin"/"Melaghlin", which is more commonly modernised "McLoughlin", "M'Loughlin", and "O'Loughlin" (among other spellings). O'Melaghlin was a phonetic rendering into Anglo-Norman and Middle English of "ó Mǽilsheáchlainn". That family is part of the historic Clann Cholmáin, a branch of the "southern" O'Neill dynasty, cousins to the northern O'Neill. Ó/Ní M(h)ǽilsheáchlainn was the surname chosen by the descendants of Máel Sechnaill II, King of Meath, 976–1022, and High King of Ireland, 979–1002 & 1014–1022. M(a)cLaughlin and M(a)cLoughlin are rarely  English forms of the surname "ó/ní Lachtna", a phonetic corruption of the much more common "Loughney" or "M(a)cLoughney". Unlike Irish surnames that have only one Gaelic source for their English form, it is not possible to tell by the spelling "McLaughlin" and other English spellings whether the person bearing the name is descended from the "Mac/Nic Lochlainn" family, the "Ó/Ní M(h)ǽilsheáchlainn" family, or the "Ó/Ní Lachtna" family. Loftus is also a branch off of the tree as they had to change their last name to gain work in England as to not be discriminated against for  being Irish