Horsepen ArmHorsepen Arm is a long second-order tributary to Marshyhope Creek in Kent County, Delaware. This is the only stream of this name in the United States.CourseHorsepen Arm rises on the Marsh Branch divide about 0.5 miles east of Anthonys Corner, Delaware, and then flows generally southeast to join Marshyhope Creek at Hollandsville, Delaware.WatershedHorsepen Arm drains of area, receives about 44.8 in/year of precipitation, and is about 6.45% forested.