Piaseczno County (Polish: powiat piaseczyński) 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 Piaseczno, which lies 17 kilometres (11 mi) south of Warsaw.

The county contains three other towns: Konstancin-Jeziorna, 8 km (5 mi) east of Piaseczno, Góra Kalwaria, 18 km (11 mi) south-east of Piaseczno, and Tarczyn, 16 km (10 mi) south-west of Piaseczno.

The county covers an area of 621.04 square kilometres (239.8 sq mi).