Seinäjoki is a city located in Southern Ostrobothnia, Finland. Seinäjoki originated around the Östermyra bruk iron and gunpowder factories founded in 1798. Seinäjoki became a municipality in 1868, market town in 1931 and town in 1960. In the beginning of 2009, the neighboring municipalities of Nurmo and Ylistaro were consolidated with Seinäjoki.
The Town library, Lakeuden Risti church and central administrative buildings are designed by Alvar Aalto.
The asteroid 1521 Seinäjoki bears the town's name.
Seinäjoki was historically called Östermyra in Swedish. Today this name is very seldom used even among the Swedish speakers. Literal translation for Seinäjoki is "Wall river".
Seinäjoki Airport is located in the neighboring municipality of Ilmajoki, 11 kilometers (10 mi) south of Seinäjoki city centre