Demyansk is an urban locality (a work settlement) and the administrative center of Demyansky District of Novgorod Oblast, Russia, located along the Yavon River. Municipally, it is incorporated as Demyanskoye Urban Settlement, the only urban settlement in the district. Population:

Demyansk was first mentioned in a chronicle in 1406 as Demon. The area was a part of Derevskaya Pyatina of Novgorod. Demon was a fortress protecting a waterway from Lake Ilmen upstream the Pola and the Yavon to Lake Seliger. The fortress was located close to the boundary between the Novgorod Republic and the Grand Duchy of Moscow, and it was at least twice sieged by Muscovite troops. In 1441, the Muscovites did not manage to conquer Demon, but in the 1470s they conquered and destroyed the fortress. After the subsequent fall of Novgorod, Demon was transferred to the Grand Duchy of Moscow. In the 17th century, Demon went into decline, and a new settlement was founded nearby, which was known as Demyansky Pogost, and later as Demyansk. In the course of the administrative reform carried out in 1708 by Peter the Great, the area was included into Ingermanland Governorate (known since 1710 as Saint Petersburg Governorate). In 1727, separate Novgorod Governorate was split off. Between 1772 and 1824, Demyansk was a part of Starorussky Uyezd of Novgorod Viceroyalty (since 1796 of Novgorod Governorate). In 1824, it was chartered and became the center of Demyansky Uyezd, which was split off Starorussky Uyezd.