Siemnocha [ɕɛmˈnɔxa] is a village in the administrative district of Gmina Lelis, within Ostrołęka County, Masovian Voivodeship, in east-central Poland. It lies approximately 6 kilometres (4 mi) south of Lelis, 8 km (5 mi) north of Ostrołęka, and 109 km (68 mi) north of Warsaw.