Gallatin River
The bulk of Missouri Headwaters State Park is found on a peninsula flanked on the east by the Gallatin River and the west by the Missouri River and the Madison River. Small parts of the park are also located on the east bank of the Gallatin River, and an island in the Missouri just below the confluence of the Madison and Jefferson Rivers. The total park size is . The Jefferson River meets the Madison and Missouri roughly midway through the park's north-south extent.