I have only just begun my family search, on both sides, so I just have family lore at this point.
My grandfather, Charles McCarron, was born in Clonmany, on the Inishowen peninsula of County Donegal, in the 1870's. He emigrated to Scotland, where my father was born. We were not the only McCarrons in Clonmany, and so we were the "Wiliams" for my great grandfather William. The area in Donegal was one where gaelic was the first language at home. My Aunt told me of going to Clonmany, from Scotland, for summer holidays as a young girl and watching my great grandparents perform many of the old celtic home rituals of prayer. I myself have never been to Clonmany, (all of my childhood visits being to Scotland, but I understand that the "old homestead" had become some sort of cultural/craft museum.My grandfather had one brother Joseph, who ended up in Spokane Washington after the First World War, but ended as a batchelor.
The town in Scotland where my grandfather went, just outside of Glasgow, was Rutherglen. It was a place many emigres from Donegal went, and I recall seeing shop signs, McCarron while I was there as a boy.
As far as other Scots connections, as a boy I was told that we were a sept of the MacDonnells of Glengary, and that was the kilt that I wore as a kid. The fact that Loch Carron is in MacDonnell country may have contributed to this. Since then I have also heard of the Grant connection and a branch of McCarrons in Argyll, (which made my mother happier than the MacDonnell connection, since she was a Campbell)However part of me feels that the whole sept system is a way of helping selling tartans! :-)