North Platte River, a river in the western United States, 680 miles (1,094 km) long. From its source in north-central Colorado, it flows north into Wyoming and then generally southeastward through Wyoming and Nebraska. It joins the South Platte River near the city of North Platte, Nebraska, to form the Platte River. Dams have been built on the North Platte for flood control, electric power, and irrigation.