Salem Township was established June 8, 1818 from Hamilton Township and originally consisted of the part of Salem south of the Little Miami and what is now Harlan Township. By a special act of the Ohio General Assembly of March 16, 1860, Harlan Township was separated from it and Salem was renamed Corwin Township. Later that year the Warren County Commissioners renamed the township Salem and took a portion of Union across the Little Miami and attached it to Salem, giving it 13,459 acres (54 km²). Salem Township is in both the Symmes Purchase and the Virginia Military District.