Mierzyn [ˈmjɛʐɨn] is a village in the administrative district of Gmina Biskupiec, within Nowe Miasto County, Warmian-Masurian Voivodeship, in northern Poland. It lies approximately 7 kilometres (4 mi) south-west of Biskupiec, 22 km (14 mi) west of Nowe Miasto Lubawskie, and 89 km (55 mi) south-west of the regional capital Olsztyn.