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 2005, the municipality of Peräseinäjoki was merged into Seinäjoki, and in the beginning of 2009, the neighbouring 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 "Wallriver".
Seinäjoki Airport is located in the neighbouring municipality of Ilmajoki, 11 kilometres (10 mi) south of the Seinäjoki city centre.
Seinäjoki is home of the Crocodiles, a professional American Football team that competes in the Finnish Maple League. The Seinäjoki Crocodiles are one of the top American Football teams in Europe.