Upper Darby High School (UDHS) is a four-year public high school located in Upper Darby Township, Delaware County, Pennsylvania, United States, as part of the Upper Darby School District. UDHS is also the oldest high school in Delaware County, having been established in 1895. As of the 2019-2020 school year, the school had an enrollment of 3,845 students and 233.23 classroom teachers (on an FTE basis), for a student-teacher ratio of 16.49.