The Marengo County History and Archive Museum is a local history museum and archive located in the historic district of Demopolis, Marengo County. The museum is housed in the historic Rosenbush building, which dates to 1895 and was a contributing property to the Demopolis Historic Business District, added to the National Register of Historic Places in 1979. It was restored in January 1979. The Marengo County Historical Society also owns other historic buildings, most notably Bluff Hall (ca. 1832), Laird Cottage (ca. 1870), and Lyon Hall (ca. 1853).

The Marengo County History and Archive Museum holds artifacts related to the history of Native American, French, African American, Jewish, and European people from Marengo County and their contributions to the local area. Archives are held there and genealogy research may be done on site. The museum and archives are run by the Marengo County Historical Society, which was founded in 1961 and has operated as non-profit since the Demopolis sesquicentennial in 1967.
The museum is located at 101 North Walnut Avenue. Nearby are Rooster Hall and Gaineswood National Historic Landmark. Rooster Hall was built originally as a Presbyterian Church in 1843 and is now owned by the city and used as an event space. Gaineswood is operated by the Alabama Historical Commission as a house museum and interprets nineteenth-century plantation life.