Lenvik in 1855
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Hillesøy is a former municipality in Troms county in Norway. It is located in the present-day municipalities of Tromsø and Lenvik and both sides of the Malangen fjord. Hillesøy included about 458 square kilometres (177 sq mi) of land with 164 square kilometres (63 sq mi) on Senja island, 263 square kilometres (102 sq mi) on Kvaløya, and 31 square kilometres (12 sq mi) of smaller islands.
Hillesøy included area on the islands of Senja and Kvaløya as well as many smaller islands such as Hillesøya and Sommarøya. On Senja island, Hillesøy included the larger villages of Fjordgård, Husøy, and Botnhamn. On Kvaløya island, it included Ersfjordbotn and Brensholmen. The island of Sommarøya is connected to the large island of Kvaløya by the Sommarøy Bridge. Most of the other islands are only accessible by boat.
The municipality is named after the old Hillesøy farm (Old Norse: Hildulfsøy) on the island of Hillesøya since that is where the Hillesøy Church was originally located. The first element of the old name comes from the old male name Hildulfr and the last part is identical with the word for "island". Another possibility for the meaning of the name is Hellisøy, where the first element comes from the work hellir which means "rock slab" and the last element again meaning "island".
The municipality of Hillesøy was established in 1855 when it was separated from the municipality of Lenvik (or it might have been in 1871–some sources do not concur). The initial population of Hillesøy was around 800 people. On 1 January 1964, Hillesøy municipality ceased to exist. The areas of Hillesøy on Kvaløya as well as all of its islands north of Hekkingen (with 1,316 inhabitants in total) became a part of the enlarged Tromsø municipality. The rest of Hillesøy on the island of Senja and the little island of Hekkingen (with a total of 1,159 inhabitants) was merged back into Lenvik.
There was a large forest fire on the island of Hillesøya in 2012 that was caused by an injured Canadian tourist attempting to light a signal fire.