Kocielnik [kɔˈt͡ɕɛlnik] is a village in the administrative district of Gmina Sadowne, within Węgrów County, Masovian Voivodeship, in east-central Poland. It lies approximately 4 kilometres (2 mi) east of Sadowne, 30 km (19 mi) north of Węgrów, and 79 km (49 mi) north-east of Warsaw.