Fort Benton is a city in and the county seat of Chouteau County, Montana, United States. Established in 1846, Fort Benton is the oldest continuously occupied settlement in Montana. Fort Benton was the most upstream navigable port on the Mississippi River System, and is considered "the world’s innermost port". The city's waterfront area, the most important aspect of its 19th century growth, was designated the Fort Benton Historic District, a National Historic Landmark, in 1961.