Ylivieska is a town and municipality of Northern Ostrobothnia region, Finland. It has a population of 15,409, and it serves as the administra…Ylivieska is a town and municipality of Northern Ostrobothnia region, Finland. It has a population of 15,409, and it serves as the administrative centre for Kalajokilaakso and Pyhäjokilaakso, an area with a population of about 90,000 inhabitants. Ylivieska is also the commercial center of the Oulu South region, the southern part of the late Oulu province.