It is 118 miles (190 km) long,[3] with headwaters in western Greene County.

The stream enters Dade County northwest of Ash Grove.

The stream meanders north into St. Clair County, passes under US Route 54 and enters the Osage River in Truman Reservoir southeast of Osceola.

[5] The Big Eddy Site, an archaeological dig, is along the Sac River within Cedar County.

Eleven feet of river sediment at the site provides a stratigraphy that suggests more than 10,000 years of nearly constant occupation by American Indians, potentially pre-dating the Clovis culture and contributing to the knowledge of the Dalton and San Patrice cultures.