Willow Street is an unincorporated community and census-designated place 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, hence the community's name. As time passed and the town grew, the road was widened and sidewalks were installed, which required the trees be removed.