The Sac River is a river in the Ozarks of Southwest Missouri. It is long, with headwaters in western Greene County. The stream passes through the northeast corner of Lawrence County then re-enters Greene County. The stream enters Dade County northwest of Ash Grove. The stream enters Stockton Lake in Dade County between Dadeville and Greenfield, then flows north exiting Stockton Lake in Cedar County. The stream meanders north into St. Clair County, passes under US Route 54 and enters the Osage River in Truman Reservoir southeast of Osceola.