Willow Street is a census-designated place (CDP) in Lancaster County, Pennsylvania, United States. The population was 7,578 at the 2010 census. In the early part of the 20th century the main thoroughfare in town was lined with willow trees on both sides for the length of the town. The community received its name because of these trees. As time marched on the town grew. The road was widened, sidewalks were installed which required the trees be removed.