History of Scottish Gaelic
All surviving dialects are Highland and/or Hebridean dialects. Dialects of Lowland Gaelic have become defunct since the demise of Galwegian Gaelic, originally spoken in Galloway, which seems to have been the last Lowland dialect and which survived into the Modern Period. By the 18th century Lowland Gaelic had been largely replaced by Lowland Scots across much of Lowland Scotland. According to a reference in "The Carrick Covenanters " by James Crichton, the last place in the Lowlands where Scottish Gaelic was still spoken was the village of Barr in Carrick: only a few miles inland to the east of Girvan, but at one time very isolated. Crichton gives neither date nor details.
Celts
Today, the term Celtic generally refers to the languages and respective cultures of Ireland, Scotland, Wales, Cornwall, the Isle of Man, and Brittany, also known as the Celtic nations. These are the regions where four Celtic languages are still spoken to some extent as mother tongues. The four are Irish Gaelic, Scottish Gaelic, Welsh, and Breton; plus two recent revivals, Cornish (one of the Brittonic languages) and Manx (one of the Goidelic languages). There are also attempts to reconstruct Cumbric, a Brittonic language from North West England and South West Scotland. Celtic regions of Continental Europe are those whose residents claim a Celtic heritage, but where no Celtic language has survived; these areas include the western Iberian Peninsula, i.e. Portugal and north-central Spain (Galicia, Asturias, Cantabria, Castile and León, Extremadura).