Grójec County 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 Grójec, which lies south of Warsaw. The county contains three other towns: Warka, east of Grójec, Nowe Miasto nad Pilica, south-west of Grójec, and Mogielnica, south-west of Grójec.