A 2016 statistical comparison of municipalities was rated for health and viability. Exceptionally good results were found in violent crime. The original Finnish name Mustasaari have been a medieval island. The parish is mentioned first in 1348 as Mustasaari parish. Swedish developed although the form Mustasaari into Mussor. The mid-14th century Saint Mary's Church was built in Korsholm island. The whole of Ostrobothnia was governed from Korsholma Castle for hundreds of years.