Vaasa Province followed by Western Finland Province
The Province of Vaasa (Finnish: Vaasan lääni [ˈʋɑːsɑn ˈlæːni]; Swedish: Vasa län, Finland Swedish: [ˈvɑːsɑ ˈleːn], Sweden Swedish: [ˈvɑ̂ːsa ˈlɛːn]) was a province of Finland, established in 1775 when Finland was an integrated part of Sweden from the southern part of Ostrobothnia County and disbanded in 1996. The province was named after the city of Vaasa.
On the death of Tsar Nicholas I in 1855, a small group of citizens in the city of Vaasa tendered a petition to change the name of the city after him. The name of the city came from the Royal House of Vasa and despite that only 15 citizens were backing the proposal the name of the city was changed to Nikolaistad (Russian: Николайстада, Finnish: Nikolainkaupunki).
In 1960 the eastern part was separated as the Province of Central Finland. In 1997 it was reunited with Central Finland, together they merged with the northern part of the Province of Häme and the Province of Turku and Pori to establish the new Province of Western Finland. 
The former province corresponds to the current regions of Ostrobothnia, Central Ostrobothnia and Southern Ostrobothnia.