|Length||70.0 km (43.5 mi)|
|West end||National Route 4 in Utsunomiya|
|East end||National Route 118 in Mito, Ibaraki|
Route 123 was originally designated on 18 May 1953 from Chiba to Mito. This was redesignated Route 51 on 1 April 1963 and the current Route 123 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.
- Media related to Category:Route 123 (Japan) at Wikimedia Commons