Alajärvi is a municipality of Finland.

It is located in the province of Western Finland and is part of the Etelä-Pohjanmaa region. The municipality has a population of 9253 and covers an area of 768,37 km² of which 30,19 km² is water. The population density is 12,380 inhabitants per km².

The municipality is unilingually Finnish.

See also: Municipalities of Western Finland