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

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

Its administrative seat and largest town is Płońsk, which lies 63 kilometres (39 mi) north-west of Warsaw.

The only other town in the county is Raciąż, lying 25 km (16 mi) north-west of Płońsk.

The county covers an area of 1,383.67 square kilometres (534.2 sq mi).