Perniö is a former municipality in the Southwest Finland region of Finland. It was consolidated with the city of Salo on January 1, 2009, and is now part of Salo rather than an independent municipality.
Before the merger, Perniö bordered the municipalities of Ekenäs, Halikko, Kimito, Kisko, Muurla, Salo and Särkisalo. Its location in the southwest of the country places it within the broader Southwest Finland region, an area that includes the coastal and inland districts around Salo.