The municipality has a population of and covers an area of of which is water. The population density is. The municipality is bilingual, with a majority being Swedish and a minority Finnish speakers. The Finnish speakers are concentrated near the enclosed city Vaasa, particularly in Smedsby, and in the villages of Toby and Kvevlax in the southern plain, while the rest of the municipality is Swedish-speaking. In a 2016 statistical comparison of municipalities by Yle, Korsholm was rated 5/5 for viability and health and 4/5 for atmosphere, but only 2/5 for economy. Exceptionally good results were found in violent crime, which occurs at a rate of 1.9 per 1,000 inhabitants vs. the national average of 5.6, in the number of alcoholics and other addicts, at 0.6 per 1,000 inhabitants, vs. the national average of 3.3, and the proportion of youth smoking at 6.0%, vs the national average of 14.2%. Concerns were mainly economic: the employment self-sufficiency is only 57% vs. 89%, the equity ratio is poor and indebtedness is relatively high, despite the municipal tax being the same as the national average. Korsholm has relatively little industry and commuting to Vaasa is very common. Korsholm is neither losing nor gaining inhabitants by migration.
History
Name
The original Finnish name Mustasaari "Black Island" may have been a medieval island cleared by a wildfire or an island that looks dark when approaching from the sea. Due to isostatic uplift, the area referred to is now inland. The parish is first mentioned as Mustasaari parish in 1348. In Swedish, the pronunciation developed into Mussor, although the form Mustasaari remained in use in the community. Mikael Agricola, the founder of written Finnish, spelled it Mustsåår in 1530. Olaus Magnus spelled it as Mostesar in his 1539 map, Carta Marina, where the castle appeared separately as "Korsholm". In 1606–1611, it was known as Mussar, but in 1611 the city of Vaasa was founded in the parish and thus the parish was known as Vaasa. In 1772, it was known as "city of Vaasa and Mustasaari annex", and in 1807–1867 "parish of Vaasa and Mustasaari". Since then, Vaasa has been an independent parish. The municipality was named Korsholm in Swedish in 1927, after the medieval Korsholma castle.
Middle Ages
Korsholm has a history that can be dated back to 1348. In that year Korsholm was mentioned for the first time in writing in a royal letter concerning freedom of commerce. Therefore, the municipality celebrated its 650th anniversary in 1998. In the mid-14th century Saint Mary's Church was built in Korsholm island. The whole of Ostrobothnia was governed for hundreds of years from Korsholma Castle. The ruins of Saint Mary's Church and Korsholm Castle are now in the old town of Vaasa.
1973 merger
Today's Korsholm municipality consists of five smaller municipalities that were merged in 1973: Korsholm in the center, Replot and Björköby in the far archipelago, Solf in the southern plain and Kvevlax in the eastern plain. To reflect the new, larger municipality the motif in the Korsholm coat of arms is five intertwined golden threads on a red background.
