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.
Isle of Arran
Gaelic was still spoken widely on Arran at the beginning of the 20th century. The 1901 Census reported 25–49 per cent Gaelic speakers on the eastern side of the island and 50–74 per cent on the western side of the island. By 1921 the proportion for the whole island had dropped to less than 25 per cent. However, Nils Holmer quotes the Féillire (a Gaelic almanack) reporting 4,532 inhabitants on the island in 1931 with 605 Gaelic speakers, showing that Gaelic had declined to about 13 per cent of the population. It continued to decline until the last native speakers of Arran Gaelic died in the 1990s. Current Gaelic speakers on Arran originate from other areas in Scotland. In 2011, 2.0 per cent of Arran residents aged three and over could speak Gaelic.