Des Moines is the capital and the most populous city in the U.S. state of Iowa. It is also the county seat of Polk County. A small part of the city extends into Warren County. It was incorporated on September 22, 1851, as Fort Des Moines, which was shortened to "Des Moines" in 1857. It is located on, and named after, the Des Moines River, which likely was adapted from the early French name, Rivière des Moines, meaning "River of the Monks".