History of King's Highway 40C:
King's Highway 40C is one of Ontario's most peculiar and mysterious highway routes. After the new Sarnia Bypass opened to traffic in the 1960s, Highway 40 was removed from its original route through Downtown Sarnia and rerouted along the new Sarnia Bypass. This resulted in several changes to the highway route numbers through Sarnia. The former branch route of Highway 40 that followed Cromwell Street and Front Street became Highway 40C in 1963. The old route of Highway 40 through Sarnia via Chistina Street was renumbered as Highway 40B soon thereafter. During 1964, the route of Highway 40C was extended slightly into nearby Point Edward so that it connected with Highway 402. The extension of Front Street between Exmouth Street and Highway 402 was designated as Highway 40C on February 6, 1964.
The 1965 Ontario Official Road Map seems to imply that Highway 40C only ran along the section of Front Street between Exmouth Street and Highway 402. However, Department of Highways (DHO) mileage tables from the same period show that Highway 40C did indeed continue south along Front Street from Exmouth Street into Downtown Sarnia. The mileage tables have been assumed to be correct, since the mileage shown for the highway is more or less consistent over a period of several years. The route of Highway 40C was apparently decommissioned sometime in 1969, since the route is shown in the 1968 DHO mileage table, but was omitted from the 1970 DHO mileage table. However, it should be noted that all but 250 metres of Highway 40C followed municipal streets that were not under DHO's jurisdiction, which makes is hard to determine exactly how long the route of Highway 40C was actually signed for. Highway 40C was one of only three "C" suffixed highway route numbers in Ontario. The other two routes were Highway 3C near Fort Erie and Highway 7C near Peterborough.