Soini is a municipality in Finland, located in the South Ostrobothnia region. It is a sparsely populated rural area in the western part of the country.
The municipality covers an area of 574.22 square kilometres (221.71 sq mi), of which 22.17 square kilometres (8.56 sq mi) is water. Its population is 1,772, giving a population density of 3.21 inhabitants per square kilometre (8.3/sq mi).