Barumun River is a Sumatran river that begins in Siraisan, Padang Lawas Regency in the southeastern North Sumatra, Indonesia, about 1,200 km northwest of the capital Jakarta.

[3][4] The river flows northward through North Padang Lawas, South and Labuhan Batu Regency before reaching Sumatra's east coast with its estuary in Malacca Strait.

The largest city on the Barumun is Kotapinang, in South Labuhan Batu Regency, with a population of 68,943 people in mid 2023.

While the largest city in the Barumun River basin is Rantau Prapat (in Labuhan Batu Regency), which is located on the Bilah tributary with a population of 177,912 people in mid 2023.

Tributaries include the Bilah, Kanan, Batang Pane, Sihapas and Aek Sangkilon.