Siikajoki is a municipality of Finland. It is located in the province of Oulu and is part of the Northern Ostrobothnia region. The municipality has a population of 5,519 (30 June 2015) and covers an area of 1,653.96 square kilometres (638.60 sq mi) of which 601.94 km (232.41 sq mi) is water. The population density is 5.25 inhabitants per square kilometre (13.6/sq mi). Neighbour municipalities are Hailuoto, Liminka, Lumijoki, Raahe and Siikalatva.