The town of Vaasa was founded in Korsholm parish in 1606 and today the municipality completely surrounds the city.

The municipality consists of the central areas, the southern plain, and the extensive archipelago.

Parts of the archipelago belong to the UNESCO World Heritage Site of Kvarken.

Olaus Magnus spelled it as Mostesar in his 1539 map, Carta Marina, where the castle appeared separately as "Korsholm".

In that year Korsholm was mentioned for the first time in writing in a royal letter concerning freedom of commerce.

To reflect the new, larger municipality the motif in the Korsholm coat of arms is five intertwined golden threads on a red background.

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,[6] Korsholm was rated 5/5 for viability and health and 4/5 for atmosphere (concerning e.g. education, crime and leisure), but only 2/5 for economy.

Concerns were mainly economic: the employment self-sufficiency is only 57% vs. 89%, the equity ratio is poor (34.8% vs. 51.9%) and indebtedness is relatively high (70.4% vs. 48%), despite the municipal tax being the same as the national average (20.75%).