The Coldwater River is a 19.4 mi stream in the U.S. state of Michigan. Located in western Michigan, the river is a part of the Grand River drainage basin. The Coldwater River flows through Barry and Kent counties, and the drainage basin also includes a large portion of southwest Ionia County and a tiny portion of Sunfield Township in the northwest corner of Eaton County. The Coldwater is formed from the Little Thornapple River in Carlton Township in Barry County. It flows northerly for a few miles and then flows mostly west until emptying into the Thornapple River in southern Caledonia Township at 42.77472°N, -85.46056°W. Major tributaries (from the mouth):