A John MacHaggart appears in the 1881 English Census boarding in West Ham, Essex, and Two MacIlhaggers, John and Archie, appear in the 1906 Canada Census in a place called Assiniboia, Saskachewan. There are two other baptisms, of John MacHaggart and Margaret MacIlhagga both in 19th Century Ireland. Margaret, daughter of Archibald, married Joseph Adams in Belfast in 1915. Another Margaret MacIlhaggart (a widow) married Joseph Hills in Ballymena in 1903. However, I know this to be a mistranscription.
And now, in the 'findmypast' website I have found June MacIlhaggie who in the April-June Quarter of 1963 married David W. Howes in Chelmsford, Essex, and I have to confess that I have no idea how June fits into a clan family. There is only one 'June' in my Birth Index, namely June McIlhagga, daughter of Samuel who died in 2009 and whose burial in Ballee Cemetery, County Antrim, was reported in the Belfast Telegraph. At the time of her death she was June Miller (nee McIlhagga) and must I think have been born in the 1930s.
If anyone knows of any other instances, I would be interested to know about them. There is of course no difference between 'Mc' and 'Mac', and neither is more 'correct' than the other, and both get abbreviated in documents, especially in old handwriting, to M'.