Kierzek [ˈkʲɛʐɛk] is a village in the administrative district of Gmina Kadzidło, within Ostrołęka County, Masovian Voivodeship, in east-central Poland. It lies approximately 10 kilometres (6 mi) west of Kadzidło, 25 km (16 mi) north-west of Ostrołęka, and 115 km (71 mi) north of Warsaw.