Demopolis is the largest city in Marengo County, in west-central Alabama. The population was 7,162 at the 2020 census.

The city lies at the confluence of the Black Warrior River and Tombigbee River. It is situated atop a cliff composed of the Demopolis Chalk Formation, known locally as White Bluff, on the east bank of the Tombigbee. It is at the center of Alabama's Canebrake region and is also within the Black Belt region.

Demopolis was founded in the early 1800s after the fall of Napoleon's empire. It was named by a group of French expatriates, a mix of exiled Bonapartists and other French refugees who had settled in the United States after the overthrow of the colonial government in Saint-Domingue by enslaved workers. Napoleon had sent troops there in a last attempt to regain control of the island, but they were defeated, largely by high mortality due to yellow fever.

The name, meaning in Greek "the People's City" or "City of the People" (from Ancient Greek δῆμος + πόλις), was chosen to honor the democratic ideals behind the endeavor. First settled in 1817, it is one of the oldest continuous settlements in the interior of Alabama. French colonists had founded Mobile on the coast in the early 18th century. Demopolis was incorporated on December 11, 1821.