The Niobrara River is a tributary of the Missouri River, approximately 430 mi (692 km) long, running through the U.S. states of Wyoming and Nebraska. The river drains one of the most arid sections of the Great Plains, and has a low flow for a river of its length.

It rises in the High Plains of eastern Wyoming, in southern Niobrara County, Wyoming. It flows east as an intermittent stream past Lusk and southeast into northwestern Nebraska. It flows southeast across the Pine Ridge country of Sioux County, then east through Agate Fossil Beds National Monument, past Marsland, and through Box Butte Reservoir. It flows east across northern Nebraska, near the north edge of the Sandhills, past Valentine. It is joined by the Snake River about 13 mi (21 km) southwest of Valentine. In north-central Nebraska it is joined by the Keya Paha River approximately 6 mi (10 km) west of Butte. It joins the Missouri northwest of Niobrara in northern Knox County.

Two sections of the Niobrara River in central Nebraska have been designated as the Niobrara National Scenic River.

Between 1861 and 1882, the stretch of the Niobrara River from the mouth of the Keya Paha its confluence with the Missouri marked the boundary between Nebraska and the Dakota Territory.

See also

• List of Nebraska rivers
• List of Wyoming rivers

Rivers of Nebraska | Rivers of Wyoming | Tributaries of the Missouri River