The Round Barn, Washington Township is a historic building located south of Janesville, Iowa in Black Hawk County, United States. It was built in 1917 as a dairy barn. The building is a true round barn that measures 60 feet (18 m) in diameter.[2] The structure is constructed in clay tile and features an aerator and a two-pitch roof. It was built around a silo with a water tank on top of it. While that is typical of this type of structure, it is the only one known to exist in Iowa.[3] It has been listed on the National Register of Historic Places since 1986.[1]