The Dearborn 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...

, approximately 70 mi (113 km) long, in western Montana

Montana

Montana is a state in the Western United States. The western third of Montana contains numerous mountain ranges. Smaller, "island ranges" are found in the central third of the state, for a total of 77 named ranges of the Rocky Mountains. This geographical fact is reflected in the state's name,...

 in the United States

United States

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

. It rises in the Lewis and Clark National Forest

Lewis and Clark National Forest

Lewis and Clark National Forest is located in west central Montana, United States. Spanning , the forest is managed as two separate zones. The eastern sections, under the Jefferson Division, is a mixture of grass and shrublands dotted with "island" pockets of forested areas. Here, cattle leases to...

, near Scapegoat Mountain in the Lewis and Clark Range

Lewis and Clark Range

The Lewis and Clark Range, el. , is a small mountain range southwest of Seeley Lake, Montana in Powell County, Montana....

 of the Rocky Mountains

Rocky Mountains

The Rocky Mountains are a major mountain range in western North America. The Rocky Mountains stretch more than from the northernmost part of British Columbia, in western Canada, to New Mexico, in the southwestern United States...

 at the continental divide

Continental divide

A continental divide is a drainage divide on a continent such that the drainage basin on one side of the divide feeds into one ocean or sea, and the basin on the other side either feeds into a different ocean or sea, or else is endorheic, not connected to the open sea...

, in western Lewis and Clark County

Lewis and Clark County, Montana

-National protected areas:* Flathead National Forest * Helena National Forest * Lewis and Clark National Forest * Lolo National Forest * Rocky Mountain Front Conservation Area -Demographics:...

. It flows generally southeast through secluded canyon

Canyon

A canyon or gorge is a deep ravine between cliffs often carved from the landscape by a river. Rivers have a natural tendency to reach a baseline elevation, which is the same elevation as the body of water it will eventually drain into. This forms a canyon. Most canyons were formed by a process of...

s, and joins the Missouri near Craig

Craig, Montana

Craig is an unincorporated community in Lewis and Clark County, Montana, United States. Craig is located along Interstate 15 north of Helena....

.

It is crossed by the Dearborn River High Bridge, which was constructed in 1897.

It is a popular destination for whitewater rafting and fly fishing

Fly fishing

Fly fishing is an angling method in which an artificial 'fly' is used to catch fish. The fly is cast using a fly rod, reel, and specialized weighted line. Casting a nearly weightless fly or 'lure' requires casting techniques significantly different from other forms of casting...

. Whirling disease has become a significant problem among trout

Trout

Trout is the name for a number of species of freshwater and saltwater fish belonging to the Salmoninae subfamily of the family Salmonidae. Salmon belong to the same family as trout. Most salmon species spend almost all their lives in salt water...

in the river.

The Dearborn is a Class I river for stream access for recreational purposes from the highway 431 bridge to its confluence with the Missouri river.