Österåker Municipality (Swedish: Österåkers kommun, IPA: [ˈœ̂sːtɛrˌoːkɛʂ kʊˈmʉːn]) is a municipality in Stockholm County in east central Sweden. Its seat is located in the town of Åkersberga, with a population of 26,727 (2005).

From 1974 to 1982 Österåker was part of Vaxholm Municipality.

Its location by the Stockholm archipelago, in the Roslagen area, attracts both people who settles here, often commuting to Stockholm, and visiting tourists. Österåker boasts several golf courses, many possibilities for canoeing, horse riding, fishing and other nature activities.

Österåker also has a historical significance, with at least three notable castles from the 17th and 18th centuries, with histories tracing even further back. Sweden's once largest quartz mine, the Härsbacka mine, lays within the municipality.^[3]

Like many other municipalities making up Metropolitan Stockholm, Österåker has a significant outward-commuting mainly to Stockholm, with some 13,000 commuters.

Of the 800 islands and islets, the largest one is Ljusterö, a community of its own covering the eastern side of the mainland, and accessible by car. Easy access is granted by regular ferries, including one old steam ship from 1898. Other major islands are Finnhamn, Husarö and Ingmarsö.

Elections to Swedish municipals are held every fourth year on the third Sunday in September. The 2022 election to the 51-seat council resulted in the centre-right majority of four parties (M, L, KD and C) staying in power.

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Österåker is served by the Stockholm public transport system through SL. There are six stops on the narrow gauge Roslagsbanan suburban railway and buses to Stockholm and Norrtälje as well as an extensive internal bus network.