The Muskegon River is a 216-mile-long river in the Lower Peninsula of the U.S. state of Michigan. From its source at Houghton Lake in Roscommon County, the river flows in a generally southwesterly direction to its mouth at Lake Michigan at the eponymous city of Muskegon. The river drains an area of 2,350 square miles, and collects a number of tributaries, inclu…The Muskegon River is a 216-mile-long river in the Lower Peninsula of the U.S. state of Michigan. From its source at Houghton Lake in Roscommon County, the river flows in a generally southwesterly direction to its mouth at Lake Michigan at the eponymous city of Muskegon. The river drains an area of 2,350 square miles, and collects a number of tributaries, including the Little Muskegon River, Hersey River, and Clam River.