Frösön (Frey's island; Swedish pronunciation: [fɾøːsøːn]; [fɾøːsœʏːa] in the local dialect, Jamtlandic) is a small island in the lake Storsjön located west of the city Östersund in Jämtland. For ages this island was the regional centre of Jämtland.
Frösön is the location of "Frösöstenen", the northernmost runestone in the world, dating from 1030-1050 AD. Frösön was a separate köping until 1974 but was merged with Östersund at that time.
The island is named after Freyr, the Norse God of fecundity and love.
The Swedish composer Wilhelm Peterson-Berger had a summer house (and from 1930 a permanent home) on the island. In 1896 Peterson-Berger composed a set of piano pieces entitled Frösöblomster (Flowers of Frösön), and his opera Arnljot from 1910 is partly based on the runic inscriptions on Frösö Runestone.