a city and the county-seat of Cass county, Nebraska, U.S.A., situated in the valley and on the bluffs of the Missouri river near the mouth of the Platte. Pop. (1900), 49 6 4, of whom 979 were foreign-born. It is served by the Chicago, Burlington & Quincy, and the Missouri Pacific railway systems. There are railway car-shops, and a considerable trade is done in grain and cattle. A trading-post licensed by the United States government was opened here in 1853, and a town platted in 1854. Plattsmouth was first incorporated as a city in 1855, being one of the oldest settlements and cities of the state.