Soini is a municipality of Finland. It is located in the Southern Ostrobothnia region. The municipality has a population of 1,873 and covers an area of 574.22 square kilometres (221.71 sq mi) of which 22.17 km2 (8.56 sq mi) is water. The population density is 3.39 inhabitants per square kilometre (8.8/sq mi).

South Ostrobothnia is one of the 19 regions of Finland. It borders the regions of Ostrobothnia, Central Ostrobothnia, Central Finland, Pirkanmaa, and Satakunta. Among the Finnish regions, South Ostrobothnia is the ninth largest in terms of population. Seinäjoki is the regional centre and by far the largest city in the area.