Three Forks is a city in Gallatin County, Montana, United States. The population was 1,728 at the 2000 census. Three forks is named because it lies near the point, in Missouri Headwaters State Park, where the Jefferson, Madison and Gallatin Rivers form the Missouri.

The Indian woman Sacajawea is best known as the interpreter and guide for the Lewis and Clark Expedition. In 1800, she was captured by the Mennetaree tribe near the present site of Three Forks. She later returned to this area with Lewis and Clark and the Corps of Discovery.