Birpur is a city and a notified area in Supaul district in the state of Bihar, India. It is a small town on the Indo-Nepal border near the historic Koshi Barrage on the Koshi River. It has an airstrip, which is being modernised and later on will be utilized for commercial as well defence use. It had been made when first prime minister of India Jawaharlal Nehru had landed here to lay the foundation stone of Koshi Barrage. There has been a new helipad constructed next to the airstrip for multi purpose use.