Wikipedia
McLoughlin
McLoughlin is one of nearly two dozen Anglicisms for three Gaelic- Irish surnames: Mac/Nic Lochlainn (most commonly Anglicised McLaughlin, Ó/Ni Máoilsheáchlainn (usually McLoughlin or M'Loughlin), and Mac/Nic Lochnaigh (usually rendered Loughney but occasionally McLoughlin or MacLoughlin.
Mac and Ó are masculine prefixes; Ni/Nic is feminine. Mac is rendered into English as Mac, Mc and M'. Ó is rendered ''O' ''. The feminine prefix is rendered into English according to its masculine counterpart (e.g. Nic na Mhara > McNamara, Ni hEaghra > O'Hara). They are used with names that originated as patronymics. Occasionally, the prefix Mael/Maol is Anglicised Mac/Mc.