Koski Tl is a municipality in Finland, located in the Southwest Finland region. It is one of the smaller municipalities in that part of the country, situated in the inland area of the region rather than on the coast.
The "Tl" in its name is an abbreviation of the Finnish word "Turun lääni," referring to the historical Province of Turku and Pori, and it serves to distinguish the municipality from other Finnish places also named Koski. The municipality is a rural community, and Finnish is its sole official language.