Posio is a municipality of Finland. It is located in the province of Lapland. The municipality has a population of 2,923 and covers an area of 3,544.90 square kilometres of which 506.14 km2 is water. The population density is 0.96 inhabitants per square kilometre. Neighbour municipalities are Rovaniemi, Kemijärvi, Ranua, Salla, Kuusamo, Taivalkoski and Pudasjärvi. The municipality has a single language, Finnish.