The Round Barn, Millville Township is an historical building located in rural Clayton County, Iowa, United States. It was built in 1916 as a general purpose barn. The building is a true round barn that measures 72 feet (22 m) in diameter.[2] It is covered in metal vertical siding and features a dome roof, a cupola with an aerator and a central silo.[3] It is one of three round barns extant in Iowa known to have a dome roof.[2] The barn has been listed on the National Register of Historic Places since 1986.[1]