The Old Alexander House is a historic house in rural Columbia County, Arkansas. Built in 1855 by Samuel Alexander, this single-story dogtrot house is one of the oldest buildings in the county, and one of its few surviving antebellum structures. It is located on what was once the main road between Camden, Arkansas and Shreveport, Louisiana, northeast of Magnolia. The house remains in the ownership of the Alexander family, who use it as a family museum. The house was listed on the National Register of Historic Places in 1979.