Haapajärvi is a municipality of Finland. The municipalities (kunta in Finnish, kommun in Swedish) represent the local level of self government in Finland and also act as the basic regional administrative units of the country. ...

It is located in the province of Oulu and is part of the Northern Ostrobothnia region. The municipality has a population of 8,083 and covers an area of 789.71 km² of which 8.18 km² is water. The population density is 10.2 inhabitants per km². Finland consists of 6 provinces (Finnish: läänit, Swedish: län), following a 1997 redesign that reduced their number from 12. ... Northern Ostrobothnia is a region (maakunta / landskap) of Finland. ... Finland is divided into 20 regions (maakunta/landskap in Finnish/Swedish). ...

The municipality is unilingually Finnish.