59°01′01″N 17°53′11″E / 59.01699°N 17.88637°E / 59.01699; 17.88637

Södertörn is a roughly triangular peninsula and artificial island^[1] in eastern Södermanland, Sweden, with an area of 1,207 km² and is bordered by:

• Lake Mälaren, the Hammarby Canal and the inlet of Saltsjön (a part of the Baltic Sea) to the north,
• The Baltic Sea (the Stockholm Archipelago) to the east and the south,
• Himmerfjärden and Hallsfjärden (parts of the Baltic Sea) to the west as well as
• The Södertälje Canal to the northwest.

The Södertälje Canal and Hammarby Canal are man-made waterways, so the peninsula of Södertörn is not fully separated from (the rest of) the Swedish mainland or the island of Södermalm by nature.^[2] The area is classified as an island by Statistics Sweden, making it the third largest island in Sweden.^[3]

Since 2005, the whole of Södertörn has been included in Metropolitan Stockholm. Before that, the southern parts of the island, which lie within Nynäshamn Municipality, and the western parts, which are in Södertälje Municipality, were – although in Stockholm County – not included in the metropolitan area.

The northern areas of Södertörn are to a large extent made up of rift valley countryside (and urban areas) with high ground which is either pine forest or bare. The long valleys of the south become level ground. The waters surrounding the area are either freshwater or brackish water with poor salinity. The bedrock is almost entirely gneiss.

The highest point on Södertörn is Tornberget in Haninge at 110.9 metres (363.8 feet) above sea level. It is located in Hanveden, a large area of largely coniferous forest south of Stockholm, whose eastern areas partially form the Tyresta National Park.

The southernmost parts of Södertörn were connected to Stockholm in 1901, when the Nynäs Line was opened. The railway runs between Nynäshamn in the south and Älvsjö in the north, where it joins with the main southern railway.

Södertörn was long regarded as a peninsula, but since 2014 is classified as Sweden's third largest island (after Gotland and Öland) by the Statistics Sweden, SCB. The authority justified its decision by saying that Södertälje Canal counts as so-called "surface water" and that according to the new definition, Södertörn is therefore "unequivocally" an island, surrounded by Södertälje Canal, Mälaren and the Baltic Sea.

According to SCB, Södertörn was, "if one were to stretch it, probably an island already even with the previous definition, because historically there has been water in the form of a strait or similar on the site".^[4]

The reason SCB added this, is that a large part of southern Sweden is divided from the rest of the Scandinavian Peninsula by Göta Canal, so it would also now be an island according to the last explanation. But that is not an island "because the area is not normally considered an island".

Its name (á [...] Taurinum in 1225, Tør in 1283, a Tørinne in 1383 and eventually ‘‘Södertörn’’ since 1645) derives from the Old Norse dialect word tor, meaning "broken rocky beaches", which cut deep into the coast of Södertörn.

• Botkyrka
• Haninge
• Huddinge
• Nacka (west of Skurusundet)
• Nynäshamn
• Salem
• Stockholm (the Söderort, southern, part)
• Södertälje (east of the Södertälje Canal)
• Tyresö

These municipalities are located both in Stockholm County and the province of Södermanland.

Wikivoyage has a travel guide for Södertörn.

• Södertörn University