The Vermillion River is a tributary of the Missouri River

Missouri River

The Missouri River flows through the central United States, and is a tributary of the Mississippi River. It is the longest river in North America and drains the third largest area, though only the thirteenth largest by discharge. The Missouri's watershed encompasses most of the American Great...

, 96 miles (154.5 km) long, in eastern South Dakota

South Dakota

South Dakota is a state located in the Midwestern region of the United States. It is named after the Lakota and Dakota Sioux American Indian tribes. Once a part of Dakota Territory, South Dakota became a state on November 2, 1889. The state has an area of and an estimated population of just over...

 in the United States

United States

The United States of America is a federal constitutional republic comprising fifty states and a federal district...

.

It is formed by the confluence of the East Fork Vermillion River and West Fork Vermillion River. The East Fork, approximately 103 miles (165.8 km) long, rises in Lake Whitewood in Kingsbury County

Kingsbury County, South Dakota

Kingsbury County is a county located in the U.S. state of South Dakota. As of the 2010 census, the population was 5,148. It's county seat is De Smet. It was named for two brothers, George W. and T. A. Kingsbury, who were prominently involved in the affairs of Dakota Territory and members of...

 on the Coteau des Prairies

Coteau des Prairies

The Coteau des Prairies is a plateau approximately 200 miles in length and 100 miles in width , rising from the prairie flatlands in eastern South Dakota, southwestern Minnesota, and northwestern Iowa in the United States...

. The West Fork, approximately 108 miles (173.8 km) long, rises in Miner County

Miner County, South Dakota

As of the census of 2000, there were 2,884 people, 1,212 households, and 789 families residing in the county. The population density was 5 people per square mile . There were 1,408 housing units at an average density of 2 per square mile...

. Both forks flow south, roughly parallel, joining east of Parker

Parker, South Dakota

Parker is a city in Turner County, South Dakota, United States. The population was 1,022 at the 2010 census. It is the county seat of Turner County.-Geography:Parker is located at ....

. The combined river flows south and joins the Missouri 5 miles (8 km) south of Vermillion

Vermillion, South Dakota

Vermillion is a city in and the county seat of Clay County, in the southeastern corner of the U.S. state of South Dakota, and the tenth largest city in the state. According to the 2010 Census, the population was 10,571. Vermillion lies atop a bluff near the Missouri River.The area has been home to...

.