"Gaelic has been spoken at one time or another in the whole of Scotland, barring the north of Caithness..."

It was spoken in the north of Caithness into the 20th century in Dounreay parish, and previously some other areas just to the west of Thurso. (There is evidence of past Gaelic usage in Dunnet parish, and if "the Caithness Book" is to be believed, even in Stroma, the most northerly part of Caithness.)