As of 1 October 2015[update], the fleet consists of 42 two-car E721-0 series sets (P-2 to P-44), four E721-500 series two-car sets (P-501 to P-504), and three SAT721 series two-car sets (SA101 to SA103), formed as follows with one motored (Mc) and one trailer (Tc') car.
The first E721-0 series sets were delivered from December 2006, and entered service on 1 February 2007 on Tohoku Main Line services. The first E721-500 and SAT721 series sets were delivered from February 2006 and entered service on Sendai Airport services on 18 March 2007.
The remains of sets P-1 and P-19 at Shinchi Station after the tsunami in 2011
Intermediate cars for the first two E721-1000 sets on delivery from J-TREC Niitsu in September 2016
The first of a fleet of 19 new four-car E721-1000 sets (76 vehicles in total) was introduced on 30 November 2016 on Tohoku Main Line, Joban Line, and Senzan Line services, replacing older 719 series units. The new trains are built by J-TREC, with construction shared between the company's Yokohama and Niitsu factories. These trains feature LED interior lighting.
The first four E721-1000 series intermediate cars were delivered from J-TREC's Niitsu factory to its Yokohama factory in September 2016 to be combined with driving cars built there.
^磐越西線でE721系の運転開始 [E721 series enter service on the Banetsu West Line]. Japan Railfan Magazine Online (in Japanese). Japan: Koyusha Co., Ltd. 9 March 2017. Archived from the original on 9 March 2017. Retrieved 9 March 2017.
^ abcdefghJR電車編成表 2016冬 [JR EMU Formations - Winter 2016] (in Japanese). Japan: Kotsu Shimbunsha. 18 November 2015. p. 28–29. ISBN978-4-330-62315-3.
^ abcdOne, Akihiro (February 2017). E721系1000番台 [E721-1000 series]. Japan Railfan Magazine (in Japanese). Vol. 57 no. 670. Japan: Koyusha Co., Ltd. p. 50-53.
^E721系1000番台が営業運転を開始 [E721-1000 series enters revenue service]. Japan Railfan Magazine Online (in Japanese). Japan: Koyusha Co., Ltd. 9 December 2016. Archived from the original on 4 January 2017. Retrieved 4 January 2017.
^ abcE721系1000 代新造車両の投入について [Details of introduction of new E721-1000 series trains] (pdf). News release (in Japanese). Japan: East Japan Railway Company Sendai Division. 26 May 2016. Retrieved 27 May 2016.
^E721系1000番台中間車が甲種輸送される [E721-1000 series intermediate cars transported]. Japan Railfan Magazine Online (in Japanese). Japan: Koyusha Co., Ltd. 23 September 2016. Archived from the original on 23 September 2016. Retrieved 23 September 2016.
^ abJR電車編成表 2010夏 [JR EMU Formations - Summer 2010] (in Japanese). Japan: Kotsu Shimbunsha. May 2010. p. 25. ISBN978-4-330-14310-1.
^ abcdefghijJR車両のうごき [JR rolling stock changes]. Tetsudo Daiya Joho Magazine (in Japanese). Vol. 46 no. 395. Japan: Kotsu Shimbun. March 2017. p. 127.