History of King's Highway 3B (Tillsonburg):
Tillsonburg's King's Highway 3B was created in 1973, when a new Highway 3 Bypass was completed around the southern side of Tillsonburg. The old Highway 3 route through Downtown Tillsonburg via John Pound Road, Oxford Street and Simcoe Street was briefly renumbered as Highway 3B. A portion of Highway 3B ran concurrently with Highway 19, from Broadway Street to Vienna Road. Although sections of Highway 3B remained under provincial jurisdiction until 1979, it is quite possible that the route became an unposted designation at some point in the late 1970s. Highway 3B was assigned a 7000-series highway number (Highway 7149) around 1977, so it is believed that the posting of Highway 3B route markers along the route was discontinued around that time.
After the Tillsonburg Bypass opened to traffic, most sections of Highway 3B through Tillsonburg were still under provincial jurisdiction. The only section of Highway 3B that was under municipal jurisdiction ran for a mere two blocks between London Street and Harvey Street. Beginning in 1974, additional sections of Highway 3B were transferred by the province to the Town of Tillsonburg and neighbouring Oxford County. Jurisdiction over the section of Highway 3B between Harvey Street and Goshen Street was transferred to the Town of Tillsonburg on March 27, 1974, along with the section of Highway 3B from London Street to the western limits of Tillsonburg on John Pound Road. Another 1 km section of Highway 3B was transferred from the province to the County of Oxford between the west junction of Highway 3 and the west limits of the Town of Tillsonburg, effective March 2, 1977. The final section of Highway 3B from Goshen Street to the east junction of Highway 3 was transferred to the County of Oxford, effective August 29, 1979. A different, unrelated Highway 3B existed in Windsor from 1935 up until 1997.