Nowy Dwór County (Polish: powiat nowodworski) is a unit of territorial administration and local government (powiat) in Masovian Voivodeship, east-central Poland.

It came into being on January 1, 1999, as a result of the Polish local government reforms passed in 1998.

Its administrative seat and largest town is Nowy Dwór Mazowiecki, which lies 33 kilometres (21 mi) north-west of Warsaw.

The county also contains the towns of Nasielsk, lying 21 km (13 mi) north-east of Nowy Dwór Mazowiecki, and Zakroczym, 5 km (3 mi) west of Nowy Dwór Mazowiecki.

The county covers an area of 691.65 square kilometres (267.0 sq mi).