In the early 19th century Alexander, tenth Duke of Hamilton (1767-1852) embarked on a programme of clearances that had a devastating effect on the island's population. These "improvements" typically led to the land being rented out to as many as twenty-seven families being converted into a single farm. In some cases, alternative land was promised in Canada for each adult emigrant male. In April 1829, for example, 86 islanders boarded the brig Caledonia for the two-month journey, half their fares being paid for by the Duke. However, on arrival in Quebec only 41 hectares (100 acres) was made available to the to the heads of extended families. Whole villages were removed and the Gaelic culture of the island devastated. The writer James Hogg wrote: "Ah! Wae's me. I hear the Duke of Hamilton's crofters are a' gaun away, man and mother's son, frae the Isle o' Arran. Pity on us!". A memorial to this early form of ethnic cleansing has been constructed on the shore at Lamlash, paid for by a Canadian descendant of the emigrants.

Gaelic was still spoken widely on Arran at the beginning of the 20th century. The 1901 Census reported 25-49% Gaelic speakers on the eastern side of the island and 50-74% on the western side of the island. By 1921 the percentage for the whole island had dropped to less than 25%. From then onwards, the number of speakers fell into the vague 0-24.9% bracket. 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% of the population. It continued to decline until the last native speakers of Arran Gaelic died in the 1990s. The 1.6% Gaelic speakers in the 1991 Census and the 1.5% in the 2001 Census represent Gaelic speakers from other areas settling on the island.

Arran Gaelic is reasonably well documented. Holmer carried out fieldwork on the island in 1938, reporting Gaelic being spoken by "a fair number of old inhabitants". He interviewed 53 informants from various locations and his description of the dialect, The Gaelic of Arran, was published in 1957 and runs to 211 pages of phonological, grammatical and lexical information. The Survey of the Gaelic Dialects of Scotland, which collected Gaelic dialect data in Scotland between 1950 and 1963 also interviewed 5 native speakers of Arran Gaelic.

The Arran dialect falls firmly into the southern group of Gaelic dialects (referred to as the "peripheral" dialects in Celtic studies) and thus shows:

a glottal stop replacing an Old Irish hiatus, eg rathad 'road' /r???t?/ (normally /r?a.?t?/) the dropping of /h/ between vowels e.g. athair 'father' /a??/ (normally /ah???/) the preservation of a long l, n and r, e.g. fann 'weak' /fan???/ (normally /faun??/ with diphthongisation). The most unusual feature of Arran Gaelic is the /w/ glide after labials before a front vowel, eg math 'good' /mw?h/ (normally /mah/).

Mac an Tàilleir (2003) notes that the island has a poetic name Arainn nan Aighean Iomadh - "Arran of the many stags" and that a native of the island or Arannach is also nick-named coinean mòr in Gaelic, meaning "big rabbit". Local government

From the seventeenth century to the late twentieth century Arran was part of the County of Bute. After the 1975 reorganisation of local government Arran became part of the district of Argyll and Bute in Strathclyde Region.

This two-tier system of local government lasted until 1996 when the Local Government etc. (Scotland) Act 1994 came into effect, abolishing the regions and districts and replacing them with 32 unitary authorities. Arran is now in the North Ayrshire council area, along with some of the constituent islands of the old County of Bute.

For some statistical purposes Arran is within the registration county of Ayrshire and for ceremonial purposes within the lieutenancy area of Ayrshire and Arran.

In the House of Commons, Arran has been contained since 2005 in the Ayrshire North and Arran constituency, currently represented by Katy Clark of the Labour Party. It was previously contained in the seat of Cunninghame North from 1983 to 2005, and in Ayrshire North and Bute from 1918 to 1983.