Route 115 was originally designated on 1 April 1953 from Hirashima to Niigata. This was redesignated as Route 49 on 1 April 1963 and the current Route 115 was designated the same day.
^"一般国道の路線別、都道府県別道路現況" [Road statistics by General National Highway route and prefecture] (PDF) (in Japanese). Ministry of Land, Infrastructure, Transport and Tourism. Retrieved 19 February 2020.