Posio is a municipality of Finland, located in the region of Lapland in the country's north. It is bordered by the neighbouring municipalities of Rovaniemi, Kemijärvi, Ranua, Salla, Kuusamo, Taivalkoski and Pudasjärvi.
The municipality covers a total area of 3,544.90 square kilometres (1,368.69 sq mi), of which 506.14 square kilometres (195.42 sq mi) is water. With a population of 2,826 as of 31 December 2025, Posio has a population density of 0.93 inhabitants per square kilometre (2.4/sq mi), reflecting the sparse settlement typical of the region.