Karniszyn is a village in the administrative district of Gmina Bieżuń, within Żuromin County, Masovian Voivodeship, in north-central Poland. It lies approximately 4 km north-east of Bieżuń, 11 km south of Żuromin, and 113 km 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.