Gromadzyn [ɡrɔˈmad͡zɨn] is a village in the administrative district of Gmina Sochocin, within Płońsk County, Masovian Voivodeship, in east-central Poland. It lies approximately 3 kilometres (2 mi) south-east of Sochocin, 8 km (5 mi) north-east of Płońsk, and 62 km (39 mi) north-west of Warsaw.