Three Forks is a city in Gallatin County, Montana, United States and is located within the watershed valley system of both the Missouri and Mississippi rivers drainage basins — and is historically considered the birthplace or start of the Missouri River.

The three rivers, west to east, were named by Meriwether Lewis in late July 1805 for President Thomas Jefferson, Secretary of State James Madison, and Treasury Secretary Albert Gallatin which was in the times the genesis of a mild controversy and eventually spawned a modern-day geographical controversy—in both cases regarding length comparisons between the Missouri and Mississippi rivers.

Today the two confluences are incorporated inside Missouri Headwaters State Park, which is also a U.S. National Historic Landmark.

Honored in Three Forks, the Indian woman Sacagawea is best known as the interpreter and guide for the Lewis and Clark Expedition.

The present-day city of Three Forks was founded September 17, 1908 by John Q. Adams, agent for the Milwaukee Land Company, a subsidiary of the Chicago, Milwaukee and St. Paul Railway.

[5][6][7][8] The Milwaukee Land Co., platted the town and held a lot sale that day.

Some buildings were moved to the present city from "Old Town Three Forks", a mile to the northeast.

Two banks for the town were chartered in 1909 and 1910; John Q. Adams financed construction of the latter one, the Three Valleys State Bank, whose building survives, is listed on the National Register of Historic Places, and serves as a local history museum.

The town's early growth prospects foundered from the effects of economic depression, crop failures, and an earthquake that hit the town on June 27, 1925, damaging all of its brick buildings.

Some prosperity returned during and after World War II, and population has grown modestly since.

28.4% of all households were made up of individuals, and 11.3% had someone living alone who was 65 years of age or older.

26.7% of all households were made up of individuals, and 12.1% had someone living alone who was 65 years of age or older.