Hamilton Round Barn is a historic round barn located near Mannington, Marion County, West Virginia. It was built in 1911, and is circular in shape, measuring 66 feet in diameter and 75 feet high at the center. It features a gambrel roof topped by a six-sided cupola. The barn has horizontal clapboard siding of poplar, painted white, and a slate roof. In 1985, it was one of only five round and polygonal barns standing in West Virginia.