Rusko is a municipality in the region Lounais-Suomi located in the Southwest Finland region. The municipality has a population of 6,252 (31 January 2019) and covers an area of 127.90 square kilometres (49.38 sq mi) of which 0.78 km2 (0.30 sq mi) is water. The population density is 49.18 inhabitants per square kilometre (127.4/sq mi).
The municipality is unilingually Finnish.
The municipality of Vahto was consolidated with Rusko on 1 January 2009.