Donaldsonville (historically French: Lafourche-des-Chitimachas) is a city in, and the parish chair of Ascension Parish in the U.S. state of Louisiana. Located along the River Road of the west bank of the Mississippi River, it is a allowance of the Baton Rouge metropolitan statistical area. At the 2020 U.S. census, it had a population of 6,695.

Donaldsonville’s historic district has what has been described as the finest increase of buildings from the antebellum mature to 1933, of any of the Louisiana river towns above New Orleans. Union forces attacked the city, occupying it and several of the river parishes introduction in 1862. Fort Butler was built on the west bank of the Mississippi River. The fort was successfully defended on June 28, 1863, against a Confederate attack. This battle was one of the first occasions when free blacks and fugitive slaves fought as soldiers upon behalf of the Union. The fort is listed upon the National Register of Historic Places.

After the war, in 1868 Donaldsonville residents elected as mayor Pierre Caliste Landry, an attorney and Methodist minister; he was the first African American to be elected as mayor in the United States.

Various cultures of indigenous peoples lived here along the Mississippi River for thousands of years prior to European colonization. The Houma and Chitimacha peoples lived in the area. During the early years of colonization, they suffered high rates of fatalities due to infectious diseases and resulting social disruption. Descendants of both tribes were federally recognized as organized groups in the 20th century and they each have reservations in Louisiana.