Year 826 (DCCCXXVI) was a common year starting on Monday (link will display the full calendar) of the Julian calendar, the 826th year of the Common Era (CE) and Anno Domini (AD) designations, the 826th year of the 1st millennium, the 26th year of the 9th century, and the 7th year of the 820s decade.
|Ab urbe condita||1579|
|Balinese saka calendar||747–748|
|Chinese calendar||乙巳年 (Wood Snake)|
3522 or 3462
— to —
丙午年 (Fire Horse)
3523 or 3463
|- Vikram Samvat||882–883|
|- Shaka Samvat||747–748|
|- Kali Yuga||3926–3927|
|Japanese calendar||Tenchō 3|
|Minguo calendar||1086 before ROC|
|Seleucid era||1137/1138 AG|
|Thai solar calendar||1368–1369|
952 or 571 or −201
— to —
953 or 572 or −200
- King Beornwulf of Mercia invades East Anglia, but is killed in battle. He is succeeded by Ludeca, as ruler of Mercia.
- Prince Aethelwulf, a son of King Egbert of Wessex, invades Kent, and drives out its pro-Mercian king Baldred.
- May – Euphemius, Byzantine admiral, organises an uprising in Sicily against Emperor Michael II. He proclaims himself Emperor (with the title of basileus) in Syracuse, independent from Constantinople. In turn, Euphemius is defeated by Byzantine troops (reinforcements from the East), and is driven out to North Africa.
- King Harald Klak of Denmark receives the Frisian county of Rüstringen, as a gift from Emperor Louis the Pious.
- January 22 – Montuku, emperor of Japan (d. 858)
- November 29 – William of Septimania, Frankish nobleman (d. 850)
- Al-Mubarrad, Muslim grammarian (d. 898)
- Ansgarde of Burgundy, Frankish queen (approximate date)
- Cyril, Byzantine missionary and bishop (d. 885)
- Doseon, Korean Buddhist monk (d. 898)
- Thābit ibn Qurra, Muslim astronomer and physician (d. 901)
- Ashot I, prince of Iberia (or 830)
- Ashot Msaker, prince of Armenia
- Bai Xingjian, Chinese poet and writer (b. 776)
- Beornwulf, king of Mercia
- Fujiwara no Fuyutsugu, Japanese general (b. 775)
- Heondeok, king of Silla (Korea)
- Li Guangyan, Chinese general (b. 761)
- Li Wu, prince of the Tang Dynasty
- Theodore the Studite, Byzantine abbot (b. 759)
- Wu Yantong, Chinese Buddhist monk
- Zhu Kerong, Chinese governor (jiedushi)