In Ancestry.co.uk there are 292 references to the McIlhagger spelling of our surname all of which I have entered in the Indexes I have compiled. In addition there are two references to MacIlhagger and nine to M'Ilhagger, some of which may be repeats of the more usual spelling, but I include them here for completeness so that they can be found if they do not appear elsewhere.
The two MacIlhagger references are in the 1906 Canada Census of Manitoba, Saskatchewan and Alberta, as follows:
John, Assiniboia West, Saskatchewan, born about 1878;
Archie, Assiniboia West, Saskatchewan, born about 1881.
Under the spelling M'Ilhagger there are five marriages and four births, all in Ireland and all Civil Registrations, as follows:
Mary Ann, registered 1867, Ballymena, Vol.16, page 109;
John, registered 1870, Belfast, Vol.1, page 417; spouse Mary Jane Hull;
George, registered 1876, Belfast, Vol.16, page 485, spouse Mary Jane Boyd;
David, registered Jul-Sep 1906, Belfast, Vol.1, p 320, spouse Elizabeth Louisa Sherwood;
William John, registered Apr-Jun 1908, Vol.1, p.447, spouse Eleanor M'Arthur [?].
Martha, registered 1876, Belfast, Vol.16, p 301;
Samuel Robert, registered Oct-Dec 1884, Ballinasloe, Vol.4, p.27;
Henry Joseph, registered Apr-Jun 1886, Ballinasloe, Vol.4, p.33;
Mary Kathleen, registered Jul-Sep 1887, BAllinasloe, Vol.4, p.33.