Iiyama Line

The route was built in two parts by two different owners. The section from Toyono to Tōkamachi was constructed by the private Iiyama Railway (Iiyama Tetsudō), while the section from Tōkamachi to Echigo-Kawaguchi was opened by the state-run railways as the Tōkamachi Line. The Iiyama Railway company had been founded by local promoters on 11 September 1917, but the projected cost far exceeded its capital. The project was rescued when Shin'etsu Electric (a joint venture later absorbed into Tokyo Dentō), which was planning a hydroelectric power station on the Nakatsu River feeding the Shinano River, invested heavily in the railway in order to use it to haul construction materials, taking the majority of its shares and prompting an increase in capital to fund the northward extension.

Construction proceeded in stages. The Iiyama Railway opened its first segment, Toyono to Iiyama, on 20 July 1921, then pushed downstream toward the Niigata border to carry power-station materials: Iiyama to Kuwanagawa opened on 6 July 1923, Kuwanagawa to Nishi-Ōtaki on 1 December 1923, Nishi-Ōtaki to Mori-Miyanohara on 19 November 1925, and onward to Echigo-Tazawa across 1927. Meanwhile, the government's Tōkamachi Line opened from Echigo-Kawaguchi to Echigo-Iwasawa on 15 June 1927 and on to Tōkamachi on 15 November 1927. The two systems were joined on 1 September 1929, when the Iiyama Railway completed the Echigo-Tazawa to Tōkamachi link, finishing the through route that the present Iiyama Line follows.

During the Second World War the private company was taken into state hands. On 1 June 1944 the Iiyama Railway was bought out under the wartime nationalisation programme and merged with the Tōkamachi Line; the combined Toyono to Echigo-Kawaguchi route, then 83.8 km, was renamed the Iiyama Line. Several stations were renamed or reclassified in the process, and the surviving bus and taxi operations of the former Iiyama Railway were sold off as the company was dissolved in 1945. Diesel railcars were introduced on the line from 10 November 1955, gradually displacing steam haulage.

With the breakup and privatisation of Japanese National Railways on 1 April 1987, the Iiyama Line passed to JR East, and freight operations over the whole line were discontinued at the same time; the day before, Togari Station had been renamed Togari-Nozawaonsen. Under JR East the line was modernised: tablet block working gave way to special automatic block in December 1993, and centralised traffic control with programmed route control was introduced in March 1995. One-man operation began on 1 October 1997, by which point the line's trains had all been replaced with KiHa 110 series cars, roughly ten minutes faster end to end than their predecessors.

Running almost entirely through narrow river valleys and heavy-snow country, the line has repeatedly been closed by natural disasters. The "7.11" flood of July 1995 inundated bridges and triggered landslides, suspending the entire line before it reopened in stages within a week. On 12 March 2011 the Northern Nagano earthquake caused a landslide between Yokokura and Mori-Miyanohara that washed away the trackbed, cutting the line between Togari-Nozawaonsen and Echigo-Kawaguchi; full service was restored on 29 April. The line was also closed completely by Typhoon Hagibis in October 2019, with track damage between Kaesa and Hachisu and a washout between Kita-Iiyama and Shinano-Taira, reopening section by section through 26 October. Before diesel locomotives arrived, snow was cleared by specialised "Kimaroki" formations of locomotives, Mackley ploughs and rotary snowploughs; the line still relies on avalanche fences, snow sheds and crossing heaters, and Mori-Miyanohara records a station marker commemorating the 7.85-metre snow depth measured there in February 1945.

The Iiyama Line remained a deficit local line that was once listed as a candidate for closure, but it was spared because peak directional traffic exceeded a thousand passengers an hour, winter alternative roads were poorly developed, and the line mattered to local residents. The arrival of the Hokuriku Shinkansen reshaped its northern approach: Iiyama Station was moved about 300 metres on 9 November 2014 to sit beside the new Shinkansen station, and on 14 March 2015, when the Shinkansen was extended, the parallel Shin'etsu Main Line between Nagano and Toyono was transferred to the Shinano Railway as its Kita-Shinano Line. Toyono's affiliation as a JR station thereby became the Iiyama Line, and to this day all Iiyama Line trains run through beyond Toyono over the Kita-Shinano Line to Nagano, with a couple of morning services each day continuing from Echigo-Kawaguchi over the Jōetsu Line to Nagaoka.

• 191711 September: the private Iiyama Railway Co. is established by local promoters.
• 192120 July: the Iiyama Railway opens its first section, Toyono–Iiyama.
• 19236 July: Iiyama–Kuwanagawa opens; 1 December: Kuwanagawa–Nishi-Ōtaki opens.
• 192519 November: the Iiyama Railway extends from Nishi-Ōtaki to Mori-Miyanohara.
• 192715 June: the state-run Tōkamachi Line opens Echigo-Kawaguchi–Echigo-Iwasawa; 1 August and 6 November: the Iiyama Railway extends Mori-Miyanohara toward Echigo-Tazawa; 15 November: the Tōkamachi Line reaches Tōkamachi.
• 19291 September: the Iiyama Railway opens Echigo-Tazawa–Tōkamachi, joining the Tōkamachi Line and completing the through route of today's Iiyama Line.
• 19441 June: the Iiyama Railway is nationalised under the wartime buyout, merged with the Tōkamachi Line, and the Toyono–Echigo-Kawaguchi route (83.8 km) is renamed the Iiyama Line.
• 1945February: a record snow depth of 7.85 m is measured at Mori-Miyanohara Station, commemorated by a marker at the station.
• 195510 November: diesel railcar services are introduced (Nagano–Togari), beginning the replacement of steam haulage.
• 19871 March: Togari Station is renamed Togari-Nozawaonsen; 1 April: with the breakup and privatisation of JNR, the line passes to JR East and freight operations over the whole line are discontinued.
• 199515 March: centralised traffic control (CTC) and programmed route control (PRC) are introduced; 12 July: the '7.11' flood inundates a bridge near Shinano-Asano and triggers a landslide, suspending the entire line, which reopens in stages by 18 July.
• 19971 October: one-man operation begins and all trains are replaced with KiHa 110 series cars, cutting roughly ten minutes off the end-to-end journey.
• 201112 March: the Northern Nagano earthquake causes a landslide between Yokokura and Mori-Miyanohara that washes away the trackbed, cutting Togari-Nozawaonsen–Echigo-Kawaguchi; full service resumes on 29 April.
• 20149 November: Iiyama Station is relocated about 300 m to be co-sited with the new Hokuriku Shinkansen station.
• 201514 March: with the Hokuriku Shinkansen extension, the parallel Shin'etsu Main Line between Nagano and Toyono is transferred to the Shinano Railway (Kita-Shinano Line); Toyono's JR-station affiliation becomes the Iiyama Line and through running to Nagano continues.
• 201912 October: Typhoon Hagibis (the Reiwa 1 East Japan Typhoon) closes the whole line, with mudflow between Kaesa and Hachisu and a washout between Kita-Iiyama and Shinano-Taira; service is restored section by section through 26 October.