An island of the Inner Hebrides in Argyll and Bute, Colonsay lies to the west of Jura and south of Mull. Rising to a maximum height of 143m (469 feet), the island is 8 miles (13 km) long and from 1 to 3 miles (2 and 5 km) wide with an area of 4617 ha (11,409 acres). At its southern end, Colonsay is linked to the island of Oronsay by a wide expanse of sand known as The Strand which can be crossed on foot at low tide. The island's fertile soils, derived from ancient sandstone and limestone, support a rich diversity of natural plant life as well as a range of exotic trees and shrubs imported to Kiloran Gardens near Colonsay House after Colonsay was acquired by Lord Strathcona in 1905. Prior to that date Colonsay had been owned by the MacNeills who in 1700 had exchanged lands in Knapdale with the island's owners, the Campbells of Argyll. In the 15th century the owners of the island had been the Macphees or MacDuffies, archivists to the Lords of the Isles, later to be ousted by the Macdonalds who were in turn dispossessed by the Campbells. From a peak of 387 in 1881, the island's population has steadily declined: 164 (1961), 137 (1971), 133 (1981), 98 (1991). A modest rise to 108 came about in 2001, and five new crofts were created by the island's community development company in 2010 in a bid to attract younger families.
The fictional Isle of Kiloran in the Powell and Pressburger film I Know Where I'm Going (1945), is based on Colonsay, although none of it was filmed here.
In 1965, a ferry pier was built at Scalasaig, the island's main settlement, which receives a regular ferry connecting Colonsay with Kennacraig, Islay and Oban.