Octagon, AlabamaOctagon is an unincorporated community in Marengo County, Alabama, United States. Octagon had a United States [Postal Service|post office] at one time, but it no longer exists.HistoryThe community of Octagon obtained its name from the Bethlehem Baptist Church. The first building for this church was an octagonal structure, built by George Washington Barkley and his sons after the American Civil War. At one time the community also had a Methodist church, a two-story school, general store, cotton gin, and grist mill. Only the Baptist church remains.GeographyOctagon is located at and has an elevation of.