Recorded as MacNelis, McNelis, MacNellis, McNellis and Nellis, this is an Irish surname of great antiquity. It derives from the pre 12th century Gaelic surname 'Mac Niallghuis', which loosely translates as 'The son of Neil, the vigourus one'. As to why Neil was full of vigour is unclear, but in the majority of Irish clan surnames, the origination is to do with a particular aspect of the original chief. This clan were originally from County Donegal in the far west of the country where they were coarbs, or hereditary holders of church lands and properties, at Donegal parish until about 1530. As Nellis, the surname is also quite popular in other parts of Ulster, and it is also found in some parts of Ireland as Grealish, Grealy and Greely. These spellings are apparently fused forms of the 13th century Mag Riallghuis, itself claimed to be a corrupted spelling of Mac Niallghuis. It is said that over the centuries the clan was renowned for the number of priests that it provided, no less than four to the parish of Raphoe in the 17th century. These may have included Bernard MacNellis, who was the curate of Gelncolumkille and who was apparently 'well spoken in both English and Irish' and a 'clever painter'. In the year 1609, Neal MacGnellus, another interesting spelling of the surname, was a juror at Lifford.