Mount Pleasant Township is a township in Washington County, Pennsylvania, United States. As of the 2020 census, the township population was 3,282.

Pennsylvania Route 18 is a major north–south highway in Western Pennsylvania whose southern terminus is at West Virginia Route 69 at the state line in Greene County near the village of Garrison, while the northern terminus is at PA 5 in Lake City. At a length of 205 miles (330 km), PA 18 is the only state route in Pennsylvania — north–south or east–west — to traverse the entire state. It also has the distinction of being the longest state route in Pennsylvania.