The Duchy of Pomerania-Demmin, also known as the Duchy of Demmin, and the Duchy of Dymin, was a feudal duchy in Western Pomerania within the Holy Roman Empire. Its capital was Demmin. It was ruled by the Griffin dynasty. It existed in the High Middle Ages era, between 1160 and 1264. The state was formed in 1160, in the partition of the Duchy of Pomerania, with duke Casimir I, as its first ruler. After death of its last ruler, duke Wartislaw III, the state was united with Pomerania-Stettin, forming the Duchy of Pomerania.