[4] It rises in two forks in northwestern South Dakota, in the Badlands of Butte and Harding Counties.

The North Fork rises approximately 10 miles (16 km) northeast of Crow Buttes.

The two forks flow ESE and unite near Zeona in southern Perkins County.

It joins the Missouri in Lake Oahe, with the lower 25 miles (40 km) of the river forming an arm of the reservoir.

Draining the Pierre Hills and Northern Plateaus, the Moreau (formerly Owl River) has a drainage basin of approximately 5,400 square miles (14,000 km2).