The headwaters are found in
Cypress Lake, in the
Cypress Hills, at an elevation of . It flows east towards the community of
Eastend, then turns south-east. Various reservoirs are built on its course (
Eastend Reservoir, Huff Lake, and Newton Lake) and the river is used extensively for irrigation. The river becomes
meandered as it flows through the
Grasslands National Park. Several creeks, such as Breed Creek, Little Breed Creek, and Otter Creek, flow into the Frenchman River from the
Wood Mountain Hills. After the national park and the hills, the river turns south into
Montana, where it flows into the Milk River, in
Phillips County, Montana, north of
Saco. == Fish species ==