Tjörn is the sixth largest island in Sweden, located on the Swedish west coast in the province of Bohuslän.

Bohuslän (Swedish pronunciation: [ˈbûːhʉːsˌlɛːn] is a Swedish province in Götaland, on the northernmost part of the country's west coast. It is bordered by Dalsland to the northeast, Västergötland to the southeast, the Skagerrak arm of the North Sea to the west, and the county of Østfold, in Norway, to the north. In English it literally means Bohus County, although it shared counties with the city of Gothenburg prior to the 1998 county merger and thus was not an administrative unit in its own right.