Ciemniewko [t͡ɕɛmˈɲɛfkɔ] is a village in the administrative district of Gmina Sońsk, within Ciechanów County, Masovian Voivodeship, in east-central Poland. It lies approximately 5 kilometres (3 mi) north-east of Sońsk, 10 km (6 mi) south-east of Ciechanów, and 69 km (43 mi) north of Warsaw.