St. Clair Township -- named after General Arthur St. Clair, governor of the Northwest Territory -- was one of the five original townships formed May 10, 1803. The others were Fairfield, Lemon, Liberty and Ross. In its original form, it covered about the northwestern half of the county. It included the future townships of Oxford, Milford, Wayne, Reily and Hanover. The township namesake was born in Scotland and came to American as a British soldier during the French and Indian War. St. Clair (1736-1818) remained in the colonies and rose to the rank of major general in the American army during the American Revolution. He settled in Pennsylvania after the war and was president of the Continental Congress in 1787 when the Northwest Ordinance was adopted.
Congress appointed him governor of the new Northwest Territory in 1787, and in 1791 he resumed the rank of major general and led the frontier army which built Fort Hamilton during an ill-fated campaign against the Indians in 1791.
St. Clair remained territorial governor until 1802, a year before Ohio became the 17th state.