I apologize for not completely understanding what you are looking for. Your way of referring to Church of Scotland/Presbyterian as a "state religion" is quite different from the way it has been referred to by my family and their ancestors going all the way back to their voluntary embrace of the Scottish Reformation in the 1500's. You mention a possible association your family might have had with Letterkenny, Co. Donegal, perhaps prior to settling in Fredericksburg(gh), Lennox and Addington Counties, Ottawa, Canada. If these locations refer to the McKays, the following thoughts would come to mind. Ancestry.com does not presently have census records for Lennox and Addington Counties prior to 1851. One option would be to go directly to the historical records prior to 1851 on file in these counties. If your reference to Letterkenny has to do with where the McKays lived prior to moving to Canada, I am guessing that before moving to Canada, the McKays were Scots living in Ulster. That is, the McKays would have been among those families whose ancestry originated in Lowland Scotland after the Protestant Reformation and they subsequently relocated to the northern portion of the Ireland island that became the "Ulster Plantation." Many/if not all of those moving from Scotland to the nine counties of Ulster Province were Presbyterian (i.e., Church of Scotland). When Scots moved from Ulster/Northern Ireland to Canada or the United States, "IRE" was often used to indicate where they had lived prior to the move, even though, in fact, they were Scots who had lived in Ulster Province, not "Irish" who had lived the island's Irish Republic. You wrote, "In attempt to tie the Irish to the Scots, I wrote the church with 2 simple 'general' questions." I'm not sure how you are defining "Irish" and "Scots" or what to which church you were writing, but what I would suggest is that you contact Presbyterian congregations in Letterkenny for history about their members. There are several ancestry web sites that may also be helpful, such as http://www.ulsterancestry.com/
. Best of luck!