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.
Gaels
The Gaelic languages have been in steep decline since the beginning of the 19th century, when they were majority languages of Ireland and the Scottish Highlands; today they are endangered languages. The spread of the English language has resulted in a vast majority of people of Gaelic ancestry being unable to speak a Goidelic language. As far back as the Statutes of Kilkenny in 1366, the British government had dissuaded use of Gaelic for political reasons. The Statutes of Iona in 1609 and the SSPCK in the Highlands (for most of its history) are also notable examples. As the old Gaelic aristocracy were displaced or assimilated, the language lost its prestige and became primarily a peasant language, rather than one of education and government.