This most interesting and unusual surname, found in Scotland and Ireland, has two possible origins. Firstly, it is an old Orkney surname, and is of Scottish locational origin, derived from a place called Keldall in Holm. In the modern idiom the name is also found as Kelday. However, the surname may also be of Old Gaelic origin, as one of the Anglicized forms of the Gaelic "Mac GiollaDhe", which is composed of the Gaelic refix "Mac", son of, "giolla", servant, devotee, and "De", God; hence, "the son of the follower of God". The other Anglicized forms from this source include Kildea, and Gildea. In some places these have been shortened to Gay. They were primarily a Tirconnell sept, but like so many followers of the O'Donnells, some of its families migrated to County Mayo, where, with County Donegal, it is chiefly found today. Conor, Owen, Brien and Edmund MacGillegea were adherents of Rory O'Donnell in 1601 (this being an early Anglicization of the name in County Donegal). Ballykildea (County Clare) and Ballykilladea (County Galway) are named from this sept. In Scotland, David Keldell was burgess of Kirkwall. James Kilday married Barbara Mills at Sandey, Orkney, in August 1853. The first recorded spelling of the family name is shown to be that of Audro Keldall, Caldell, a juror, which was dated 1565, in "Records of the Earldom of Orkney, 1299 - 1614", during the reign of Mary, Queen of Scots, 1542 - 1567. Surnames became necessary when governments introduced personal taxation. In England this was known as Poll Tax. Throughout the centuries, surnames in every country have continued to "develop" often leading to astonishing variants of the original spelling.