The oldest section of the Shinjuku Line is between Higashi-Murayama Station and Hon-Kawagoe Station. This section was built by the to serve as a freight feeder for the between Shinjuku and Tachikawa (now known as the Chūō Main Line). The initial Kawagoe Railway route opened between Kokubunji and Kumegawa in 1894; this portion is now known as the Seibu Kokubunji Line. Its northward extension to Kawagoe, the first part of what is now the Seibu Shinjuku Line, opened in 1895. Following several mergers and name changes between 1920 and 1922, the Kawagoe Railway became part of the Seibu Railway.