Marengo County is a county of the U.S. state of Alabama. It is named in honor of a battlefield near Turin, Italy, where the French defeated the Austrians on June 14, 1800. As of 2000 the population was 22,539. The county seat is Linden. Marengo County was created by the Alabama Territorial legislature on February 6, 1818, from land acquired from the Choctaw Indians by treaty on October 24, 1816.

The name of the county commemorates Napoleon's victory at the Battle of Marengo over the Austrian armies on June 14, 1800. This name was chosen as a compliment to the first Caucasian settlers, exiled French Bonapartists who in 1817 settled the area around Demopolis in an effort to establish a Vine and Olive Colony.