The Secrest Octagon Barn is a historic building located near Downey in rural Johnson County, Iowa, United States. It was constructed in 1883 by master builder George Frank Longerbean for Joshua Hunt Secrest as a hay barn-horse stable. The octagonal barn measures in diameter. It features red vertical siding and a sectional bell shaped roof that is supported by hand-laminated beams. The octagon-shaped cupola has the same roof shape as the barn. It was listed on the National Register of Historic Places in 1974.
According to the builder's great-grandson, the builder's name is Longerbeam.