15 July 1899 (Meiji 32) - opened by the Gan'etsu Railway as Wakamatsu Locomotive Depot (若松機関庫)
20 January 1904 (Meiji 37) - Gan'etsu Railway extended to Kitakata, turntable and water tower installed at Kitakata
21 May 1917 (Taishō 6) - renamed Aizu-Wakamatsu Locomotive Depot (会津若松機関庫), because a Wakamatsu Station already existed on the Chikuhō Main Line of the former Kyūshū Railway
15 October 1926 (Taishō 15) - first section of the Aizu Line opened (Aizu-Wakamatsu ~ Nishi-Wakamatsu ~ Aizu-Bange); engine shed at Aizu-Bange
1 November 1927 (Shōwa 2) - first section of the Yagan'u Line opened (Nishi-Wakamatsu ~ Kamimiyori)
20 November 1928 (Shōwa 3) - Aizu Line extended to Aizu-Yanaizu, engine house moved here from Aizu-Bange
23 December 1932 (Shōwa 7) - Yagan'u Line extended to Yunokami, with water tower at Kuwabara
sometime in 1932 (Shōwa 7) - Roundhouse completed at Aizu-Wakamatsu, with 15 tracks inside and 6 tracks outside
1 November 1934 (Shōwa 9) - Petrol railcars run between Aizu-Wakamatsu and Aizu-Yanaizu
27 December 1934 (Shōwa 9) - Aizu Line engine house moved from Aizu-Yanaizu to Aizu-Tajima, turntable added at Tajima
11 September 1936 (Shōwa 11) - renamed Aizu-Wakamatsu Traction Division (会津若松機関区)
18 August 1938 (Shōwa 13) - Nitchuu Line opened from Kitakata to Atsushio, with water tower and turntable (turntable removed some years later)
28 October 1941 (Shōwa 16) - Aizu Line extended to Aizu-Miyashita, with new engine house and turntable at Miyashita
sometime in 1941 (Shōwa 16) - gantry crane and coaling tower of 170 t capacity installed at Aizu-Wakamatsu
1 November 1942 (Shōwa 17) - Tadami Line opened from Koide to Ōshirakawa
sometime by 1942 (Shōwa 17) - Aizu Line and Yagan'u Line merged, collectively named Aizu Line
12 December 1947 (Shōwa 22) - Aizu Line extended from Aizu-Tajima to Arakai, turntable installed at Arakai
27 January 1949 (Shōwa 24) - single-track tankless sanding equipment installed at Aizu-Wakamatsu (tank added in 1952)
8 November 1953 (Shōwa 28) - Aizu Line extended from Arakai to Aizu-Takinohara; turntable, water tower and coaling facilities added at Takinohara, removed from Arakai
20 September 1956 (Shōwa 31) - Aizu Line extended from Aizu-Miyashita to Aizu-Kawaguchi; turntable, water tower, and coaling facilities added at Kawaguchi
30 April 1959 (Shōwa 34) - renamed Aizu-Wakamatsu Management Office (会津若松管理所)
1 June 1960 (Shōwa 35) - Aizu Management Office split into Ban'etsu Line Management Office (磐越西線管理所) and Aizu Line Management Office (会津線管理所)
20 August 1963 (Shōwa 38) - Aizu Line extended from Aizu-Kawaguchi to Tadami
6 November 1963 (Shōwa 38) - underground diesel tank installed for DCs at Aizu-Wakamatsu, with six refuelling stations
1 April 1964 (Shōwa 39) - freight service discontinued on Aizu-Kanō ~ Atsushio section of the Nitchuu Line
1 October 1965 (Shōwa 40) - "Aizu" semi-express service with DCs started (Sendai ~ Fukushima ~ Aizu-Wakamatsu ~ Aizu-Tajima); "Green Window" opened at Aizu-Wakamatsu Station
9 January 1967 (Shōwa 42) - new electric locomotive inspection shed built at Aizu-Wakamatsu in preparation for electrification of Kōriyama ~ Kitakata section of the Ban'etsu West Line
6 June 1967 (Shōwa 42) - Aizu Line Management Office and Ban'etsu West Line Management Office merged to form Aizu-Wakamatsu Operations Division (会津若松運転区)
October 1967 (Shōwa 42) - all passenger trains on Aizu Line operated with DCs
1 October 1968 (Shōwa 43) - "Aizu" semi-express renamed "Inawashiro", made three-part train between Sendai on one end and Aizu-Tajima, Tadami, and Kitakata on the other
1 September 1970 (Shōwa 45) - two underground fuel tanks installed at Aizu-Wakamatsu for filling steam generators
29 August 1971 (Shōwa 46) - Tadami Line extended from Ōshirakawa to Tadami on the Aizu Line, creating a link between the Ban'etsu West Line and the Jōetsu Line; the Nishi-Wakamatsu ~ Tadami section of the Aizu Line made part of the Tadami Line; the Aizu-Wakamatsu ~ Aizu-Takinohara section retains the name "Aizu Line"
2 October 1972 (Shōwa 47) - all passenger trains on Tadami Line operated with DCs
1 November 1972 (Shōwa 47) - freight service discontinued on Aizu-Tajima ~ Aizu-Takinohara section of the Aizu Line
30 October 1974 (Shōwa 49) - operation of steam locomotives from Aizu-Wakamatsu ends. No diesel locomotives are assigned to Aizu-Wakamatsu; rather they are deployed from Kōriyama or East Niigata
6 March 1975 (Shōwa 50) - new diesel locomotive inspection shed built
1 October 1980 (Shōwa 55) - freight service discontinued on Ōshirakawa ~ Koide section of the Tadami Line
1 December 1980 (Shōwa 55) - new route opened on Aizu Line between Kamimiyori and Yunokami in preparation for construction of the Ōkawa Dam
26 January 1981 (Shōwa 56) - new office building completed at Aizu-Wakamatsu
18 September 1981 (Shōwa 56) - request to close Nitchuu Line approved
31 March 1982 (Shōwa 57) - electric locomotive shed lengthened by 18 m
1 August 1982 (Shōwa 57) - freight service discontinued on Nishi-Wakamatsu ~ Tadami section of the Tadami Line
15 November 1982 (Shōwa 57) - "Inawashiro" express discontinued
1 November 1983 (Shōwa 58) - freight service discontinued on Kitakata ~ Aizu-Kanō section of the Nitchuu Line
1 April 1984 (Shōwa 59) - Nitchuu Line closed; passenger services replaced by the Aizu Bus Co. (会津乗合自動車)
30 May 1986 (Shōwa 61) - former freight car maintenance shed converted to truck maintenance shed
1 November 1986 (Shōwa 61) - baggage handling at Aizu-Wakamatsu Station discontinued
1 April 1987 (Shōwa 62) - JNR privatised - JR East succeeds, operating passenger trains on Aizu Line (Aizu-Wakamatsu ~ Aizu-Takinohara) and Tadami Line (Koide ~ Aizu-Wakamatsu); JR Freight operates freight trains on Aizu Line (Aizu-Wakamatsu ~ Aizu-Tajima) and Tadami Line (Aizu-Wakamatsu ~ Nishi-Wakamatsu)
16 July 1987 (Shōwa 62) - JR East passenger service on Aizu Line (Aizu-Wakamatsu ~ Aizu-Kōgen {formerly Aizu-Takinohara}) ends, replaced by Aizu Railway (会津鉄道)
11 March 1989 (Heisei 1) - renamed Aizu-Wakamatsu Transportation Division (会津若松運輸区)
16 March 1996 (Heisei 8) - Aizu-Wakamatsu freight yard closed, no further shunting occurs
1 April 1999 (Heisei 11) - JR Freight discontinues freight service on Aizu Line (Nishi-Wakamatsu ~ Aizu-Tajima) and on Tadami Line (Aizu-Wakamatsu ~ Nishi-Wakamatsu)
April 2001 (Heisei 13) - in keeping with the reconstruction of Tsuruga Castle, Aizu-Wakamatsu station building rebuilt in castle style
11 March 2011 (Heisei 23) - Tōhoku Earthquake damages the roundhouse and turntable at Aizu-Wakamatsu, rendering both unusable