Kwidzyn is a town in northern Poland on the Liwa River. With a population of 37,975, it is the capital of Kwidzyn County in the Pomeranian Voiv…Kwidzyn is a town in northern Poland on the Liwa River. With a population of 37,975, it is the capital of Kwidzyn County in the Pomeranian Voivodeship. Kwidzyn is located on the Liwa River, some 5 kilometres east of the Vistula river, approximately 70 km south of Gdańsk and 145 km southwest of Kaliningrad. It is part of the region of Powiśle.