The district (in Polish: powiat) of Piaseczno is situated in the central part of the Masovian Voivodship. It borders Warsaw from the north, the district of Otwock along the Vistula River from the east, the district of Grójec from the south and the district of Pruszków from the west. The district is divided into six communes (gminas): Góra Kalwaria, Lesznowola, Konstancin-Jeziorna, Piaseczno, Prażmów and Tarczyn.
The district lies in the strip of Central Polish Lowlands, whose land configuration was determined mainly by ice sheet and its melt-waters. It is located on the Warsaw Plain, which is a glacial plateau. The land is almost entirely flat. The major part of the district’s area is a flat plain of the bottom plateaux, changing in its south-western part into a rolling plain of very mild and low declivities (from 94 m asl in the north-eastern part near Skolimów in the commune of Konstancin-Jeziorna to 135 - 138 m asl in the south-western part near Wola Mrokowska in the commune of Lesznowola). The plain is crossed by river valleys of Jeziorka, Czarna, Utrata and their tributaries. On the glacial plateaux, there are large sand dune areas and even larger areas of sands of water origin. The largest and the highest dunes (10 – 15 m) are located in the villages of Magdalenka (the commune of Lesznowola) and Czarnów (the commune of Konstancin-Jeziorna), as well as between Aleksandrów and Cendrowice (the commune of Góra Kalwaria).
In its eastern part, the district covers the Vistula river valley, separated from the plateaux by a high (12.5 - 20 m) picturesque slope – erosion escarpment. Along the contemporary riverbed, there are fragments of a lowest meadow terrace, with deposits of river sands. The valley is dominated by a higher meadow terrace, separated from the riverbed by river embankments. The terrace reaches the level of about 2 m above the average Vistula river level and its elevation ranges between 84.8 – 94.0 m asl. It is a flat plain with small longitudinal depressions, often filled with water – so-called oxbow lakes. Along the erosion escarpment, there are fragments (between Wólka Dworska and Brześce in the commune of Góra Kalwaria, as well as between Cieciszew and Obory and in the area of Jeziorna and Bielawa in the commune of Konstancin-Jeziorna) of a medium meadow terrace of average height of 7.5 m above the Vistula river level, composed of river sands and dust deposits.
Due to land configuration and geology of the area, as well as low flow of drainage streams, about 20% of rainwater (10 – 12% in summer) per year flows out of the river basin area. It has crucial impact on soil humidity and agricultural properties.
Land configuration and geology of the area determine also the presence of groundwater, whose depth ranges between 2 m in river sand deposits and land depressions to 4 – 8 m in the areas of postglacial clay and 20 m along the erosion escarpment.
In the territory of the district, there are natural plant associations: meadows, bogs and forests. The largest meadow areas can be found in the Vistula river valley. Bogs are located mainly in the Jeziorka river valley, as well as near Solec and Baniocha in the commune of Góra Kalwaria. The forests that dominate the area of the district are coniferous forests and mixed forests. The largest forest complex in the district is the Forests of Chojnów.