Kennett Square is a borough in Chester County, Pennsylvania, United States. As of the 2020 U.S. census, Kennett Square had a population of 5,943.Kennett Square is located in the Delaware Valley and considered a suburb of both Philadelphia, the nation's sixth largest city as of 2020, and Wilmington, Delaware. The local high school is Kennett High School. The corporate headquarters of Genesis HealthCare, which administers elderly care facilities, is based in Kennett Square.