Karniszyn [karˈniʂɨn] is a village in the administrative district of Gmina Bieżuń, within Żuromin County, Masovian Voivodeship, in north-central Poland. It lies approximately 4 kilometres (2 mi) north-east of Bieżuń, 11 km (7 mi) south of Żuromin, and 113 km (70 mi) north-west of Warsaw. It is situated on the Luta River, a tributary of Wkra.

Karniszyn was a private town, administratively located in the Szreńsk County in the Płock Voivodeship in the Greater Poland Province of the Kingdom of Poland.