Grodzisk County (Polish: powiat grodziski) 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 Grodzisk Mazowiecki, which lies 29 kilometres (18 mi) south-west of Warsaw.

The county also contains the towns of Milanówek, lying 2 km (1 mi) north-east of Grodzisk Mazowiecki, and Podkowa Leśna, 8 km (5 mi) east of Grodzisk Mazowiecki.

The county covers an area of 366.87 square kilometres (141.6 sq mi).