The delta of the Torne River has been inhabited since the end of the last ice age, and there are currently (1995) 16 settlement sites known in the area, similar to those found in Vuollerim (c. 6000–5000 BC). The Swedish part of the region is not far from the oldest permanent settlement site found in Scandinavia.[1] A former hypothesis that this region was uninhabited and colonised from the Viking Age onward has now been abandoned.

Until the 19th century, inhabitants of the surrounding countryside spoke Finnish, and Kemi Sámi, a language of the Eastern Sami group, while those of the town were mainly Swedish-speaking.

The name 'Tornio' is an old Finnish word meaning "war spear": the city is named after the river.[2] To Swedish it was borrowed as Torneå after Torne å, an alternative name of the river.

The town received its charter from the King Gustavus Adolphus on May 12, 1621, and was officially founded on the island of Suensaari.[3] At that time, it was the northernmost city in the world.[4] The charter was granted in recognition of Tornio being the hub of all trade in Lapland throughout the 16th century. It was the largest merchant town in the North at the time, and for some years ranked as the richest town in Sweden. Despite the lively trade with Lapland and overseas, the population of the town remained stable for hundreds of years at little over 500.

During the 18th century Tornio was visited by several expeditions from Central Europe which came to explore the Arctic. The most notable expedition (1736–1737) was led by a member of the Académie française, Pierre Louis Maupertuis, who came to take meridian arc measurements along the Meänmaa which would show that the globe is flattened towards the poles. The church spire at Tornio was one of the landmarks used by Maupertuis in his measurements. The church was constructed in 1686 by Matti Joosepinpoika Härmä.

The Lapland trade on which Tornio depended started to decline in the 18th century, and the harbour had to be moved downriver twice as a result of the rising of the land, which made the river too shallow for navigation. However, the greatest blow to the wealth of the town came in the last war between Sweden and Russia in 1808, which saw the Russians capture and annex Finland. The border was drawn through the deepest channel of the Muonio and Tornio rivers, splitting Lapland into two parts, with deleterious effects on trade. Tornio ended up on the Russian side of the border by special request of the Russian czar. The Swedes developed the village of Haaparanta (present day Haparanda) on their side of the border, to balance the loss of Tornio, and Tornio became unilingually Finnish.

During the Russian period, Tornio was a sleepy garrison town. Trade only livened up during the Åland War (part of the Crimean War) and the First World War, when Tornio became an important border crossing for goods and people. During the First World War, Tornio and Haparanda had the only rail link connecting the Russians to their Western allies. It was also through Tornio that Vladimir Lenin returned to Russia from exile in Switzerland in March 1917.

After the independence of Finland in 1917 Tornio lost its garrison and experienced further decline, although its population increased steadily. The town played no role of importance in the Finnish Civil War, but was the scene of some fierce street fighting at the onset of the Lapland War between Finland and Nazi Germany. The rapid liberation of the town by Finnish forces may have saved it from being burned down like so many other towns in Lapland. As a result, the wooden church from 1686 can still be seen today.

After World War II, the town created new employment built on the success of the local Lapin Kulta brewery and the Outokumpu stainless steel mill. Tourism based on the border has also been a growing industry. The town is a centre of education for Western Lapland, with a vocational college and a university of applied sciences.

Tornio and Haparanda have a history as twin cities, and are currently set to merge under the names TornioHaparanda and HaparandaTornio. A new city centre is under construction on the international border and several municipal services are shared.[5] The towns also share a common golf course, situated astride the border. The IKEA store in Haparanda has signposting in Finnish as well as in Swedish, and all prices are signposted in two currencies.