 Highway 28 was assigned in 1928, when the entirety of Highway 12A was renumbered.Highway 12A was one of the original provincial highways assumed in 1919 and 1920.The Port Hope – Peterborough Road was assumed by the Department of Highways on August 11, 1920, extending from Highway 2 (Walton Street) in Port Hope to Highway 7 (George Street North) in downtown Peterborough.