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.
Language revitalization
Another Celtic language, Manx, lost its last native speaker in 1974 and was declared extinct by UNESCO in 2009, but never completely fell from use. The language is now taught in primary and secondary schools including the Bunscoill Ghaelgagh, used in some public events and spoken as a second language by approximately 1800 people. Revitalization efforts include radio shows in Manx Gaelic and social media and online resources. The Manx government has also been involved in the effort by creating organizations such as the Manx Heritage Foundation (also known as Culture Vannin) and the position of Manx Language Officer. The government has released an official Manx Language Strategy for 2017-2021.