Fredericktown is a census-designated place located in East Bethlehem Township, Washington County in the state of Pennsylvania. The community was part of the Fredericktown-Millsboro CDP for the 2000 census, but was split into two separate CDPs for the 2010 census, the other community being Millsboro. Fredericktown is located in far southern Washington County, along Pennsylvania Route 88, which travels along the Monongahela River.