The river originates at 2,375 metres (7,792 ft) above sea level in the Eastern Himalayas (the Patkai Hills)[2] in Arunachal Pradesh and flows through Tinsukia and Dibrugarh Districts in Assam to its confluence with the Brahmaputra at Dihingmukh.

Ledo, Margherita, Digboi, Duliajan and Naharkatia (Nahorkotiya) are the small towns in its valley.

[3] According to historical as well as geographical records, the Dihing once flowed through entire Upper Assam and met the Brahmaputra at Mahuramukh in Bokakhat.

The river later dried out during the 17th century (as mentioned in Buranjis) and changed course to join the Brahmaputra at Dihingmukh.

At that time the Dikhou river had an independent route and flowed as Kolong and joined the Brahmaputra at Kajalimukh in Nagaon district.