Williamston, Michigan. Williamston is a city in Ingham County in the U.S. state of Michigan. The city is at the southeast corner of Williamstown Township, but is politically independent. A portion of Williamston was annexed from adjacent Wheatfield Township. Downtown Williamston is located at the intersection of Grand River Avenue and Putnam Street (Williamston Road). The population was 3,854 at the 2010 census. Williamston is most notable for its antiques markets, and it has been promoted as a quaint, small town just outside the larger city of Lansing.