From the record
“The Frantz Round Barn is a historic building that was located near Grand Junction in rural Greene County, Iowa, United States. The true round barn measured 55 feet (17 m) in diameter.”
Wikipedia article Frantz Round Barn, CC BY-SA 4.0.
One of 16 National Register listings published here for Greene County · listed in 1986 · category: Building.
Sources: the Wikipedia article · the case file at the National Archives · the National Register database, National Park Service