The Thief River is a 40.3 miles (64.9 km) tributary

Tributary

A tributary or affluent is a stream or river that flows into a main stem river or a lake. A tributary does not flow directly into a sea or ocean...

 of the Red Lake River

Red Lake River

The Red Lake River is a river located in northwestern Minnesota. The river begins on the western side of the Lower Red Lake and flows westward. After passing through Thief River Falls, Red Lake Falls, and Crookston, the river merges with the Red River of the North in East Grand Forks. The total...

 in northwestern Minnesota

Minnesota

Minnesota is a U.S. state located in the Midwestern United States. The twelfth largest state of the U.S., it is the twenty-first most populous, with 5.3 million residents. Minnesota was carved out of the eastern half of the Minnesota Territory and admitted to the Union as the thirty-second state...

 in the United States

United States

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

. Via the Red Lake River, the Red River of the North

Red River of the North

The Red River is a North American river. Originating at the confluence of the Bois de Sioux and Otter Tail rivers in the United States, it flows northward through the Red River Valley and forms the border between the U.S. states of Minnesota and North Dakota before continuing into Manitoba, Canada...

, Lake Winnipeg

Lake Winnipeg

Lake Winnipeg is a large, lake in central North America, in the province of Manitoba, Canada, with its southern tip about north of the city of Winnipeg...

 and the Nelson River

Nelson River

The Nelson River is a river of north-central North America, in the Canadian province of Manitoba. Its full length is , it has mean discharge of , and has a drainage basin of , of which is in the United States...

, it is part of the watershed

Drainage basin

A drainage basin is an extent or an area of land where surface water from rain and melting snow or ice converges to a single point, usually the exit of the basin, where the waters join another waterbody, such as a river, lake, reservoir, estuary, wetland, sea, or ocean...

 of Hudson Bay

Hudson Bay

Hudson Bay , sometimes called Hudson's Bay, is a large body of saltwater in northeastern Canada. It drains a very large area, about , that includes parts of Ontario, Quebec, Saskatchewan, Alberta, most of Manitoba, southeastern Nunavut, as well as parts of North Dakota, South Dakota, Minnesota,...

.

Course

The Thief River flows from Thief Lake in Thief Lake Township

Thief Lake Township, Minnesota

Thief Lake Township is a township in Marshall County, Minnesota, United States. The population was 48 at the 2000 census.-Geography:According to the United States Census Bureau, the township has a total area of 36.5 square miles , of which, 27.6 square miles of it is land and...

 of northeastern Marshall County

Marshall County, Minnesota

Marshall County is a county located in the U.S. State of Minnesota. In 2010, the population was 9,439. It's county seat is Warren.-Geography:...

 and flows generally south-southwestwardly to Thief River Falls

Thief River Falls, Minnesota

As of the census of 2000, there were 8,410 people, 3,619 households, and 2,091 families residing in the city. The population density was 1,760.0 people per square mile . There were 3,931 housing units at an average density of 822.7 per square mile...

 in northwestern Pennington County

Pennington County, Minnesota

As of the census of 2000, there were 13,584 people, 5,525 households, and 3,552 families residing in the county. The population density was 22 people per square mile . There were 6,033 housing units at an average density of 10 per square mile...

. The river flows through the Agassiz National Wildlife Refuge

Agassiz National Wildlife Refuge

Agassiz National Wildlife Refuge is located in northwest Minnesota. Packs of wolves, moose, waterfowl, and 294 species of birds make this refuge a wildlife wonderland....

.

Tributaries

Thief Lake collects the Moose River

Moose River (Thief Lake)

The Moose River is a tributary of Thief Lake in northwestern Minnesota, the United States. The outflow from Thief Lake drains via the Thief River, Red Lake River, Red River of the North, Lake Winnipeg, and the Nelson River to Hudson Bay.-References:*...

, and the Thief River collects the Mud River

Mud River (Thief River)

The Mud River is a stream of northwestern Minnesota in the United States. It flows from a point east of Grygla westwards to the Agassiz National Wildlife Refuge and the large wetlands complex surrounding Agassiz Pool...

 in the Agassiz Refuge.

Name

Thief River Falls takes its name from a geographic feature, the falls of the Red Lake River at its confluence with the Thief River. The name of the river is a loose translation of the Ojibwe phrase, Gimood-akiwi ziibi, literally, the "Stolen-land river" or "Thieving Land river," which originated when a band of Dakota Indians occupied a secret encampment along the river, hence "stealing" the land, before being discovered and routed by the neighboring Ojibwe.