Without being accused of making broad blanket statements,historical Irish names like McJilton/McGilton can be somewhat broken down by religion.If you know what religion your relatives were when they came over to the US, you can make a better guess on where to start looking for them over in Ireland.
McJilton is traditionally a Scotch-Irish name. Here's what a friend of mine from N. Ireland had to say about the hostory of the Scotch-Irish.Pay close attention to the religions he mentions and maybe you can more closely locate where your ancestors were located.
"She [talking about my grandmother's family who is Scothch-Irish] would have come from what is now known as Northern Ireland comprising the Counties of Antrim; Down; Armagh; Tyrone; Londonderry and Fermansgh or perhaps Co Donegal, which though in the North, is part of the South!!! ie. the Republic of Ireland.
These Counties were largely populated from Scotland - for a variety of reasons. Some were 'planted', some were banished sheep stealers as perhaps were my forbears - or so we joke!
Many french Hugenots also came to the North of Ireland to get away from persecution - I'm half Hugenot (Methodist) and Scottish Presbyterian.
There are also many Church of Ireland - probably settlers from England. Also almost half the population is Roman Catholic - part of the reason for the conflict, which is mainly territorial.
There are 16 Mcgiltons in the N.Ireland 'Phone book. Mostly from Belfast & Co Antrim.Co Down and Co Armagh (1 each for the last two). There are no Mc Jiltons listed. So you have only 16 'phone calls to make!!!!"