Williamsville is a village in Erie County, lying mostly within the town of Amherst in the Buffalo-Niagara Falls metropolitan area, with a population of 5,423 at the 2020 census. It is named for Jonas Williams, who built the first mill on Ellicott Creek in 1811, when the settlement was called Williams Mills; his water mill still stands beside Glen Park. The village grew where the Batavia-to-Buffalo road crossed the creek just above Glen Falls, a 27-foot drop over the Onondaga Escarpment, and was incorporated in 1850. Main Street carries New York State Route 5 through the village, and Island Park, formed by an 1841 mill raceway, hosts the Old Home Days festival each summer.