Route 42 was originally designated in January 1945 as a section of Route 41 (the Kumano Highway), which ran to Tokyo. This ran concurrent with Route 1 (now Route 1/Route 23). On 18 May 1953 Route 41 was classified as a Class 2 highway and redesignated as
Route 170, which was later redesignated as Route 42 when the route was promoted to a Class 1 highway. On 1 April 1965, the classification of Class 1 and Class 2 was discontinued, redesignating it as General National Route 42. On 1 April 1993, the highway was changed by removing the section of Tsu-Matsusaka and adding the Hamamatsu - Matsusaka. This was part of the plan to connect the Atsumi Peninsula, though the Kii Peninsula, Shikoku, Kyushu and terminating at Okinawa. This plan is called the Japan Sea National Land Axis Plan. ==Passes through==