The Great Valley is a west-to-east valley through the center of Chester County, Pennsylvania, United States. It is also sometimes referred to as Chester Valley, and both names are in use throughout the region. The valley stretches from the Schuylkill River in Montgomery County in the east, southwesterly through Chester and Lancaster counties. The valley is most distinct in central Chester County, although traces of it can be followed almost the entire distance between the Delaware and Susquehanna rivers.