The municipality of Thalwil is located on the Zimmerberg ridge between the western shore of Lake Zurich and the Sihl river.
It includes the town of Thalwil, on the eastern slopes of the ridge alongside the lake, and the village of Gattikon, on the westen slopes and the bank of the Sihl.
Thalwil borders on the communes of Rüschlikon, Langnau am Albis, Oberrieden, Horgen and (across the lake) Erlenbach.

The municipality has an area of 5.5 km² (2.1 sq mi).
 Of this area, 18% is used for agricultural purposes, while 23.8% is forested.
 Of the rest of the land, 56.1% is settled (buildings or roads) and the remainder (2.2%) is non-productive (rivers, glaciers or mountains).
 In 1996 housing and buildings made up 42.3% of the total area, while transportation infrastructure made up the rest (13.7%).
 Of the total unproductive area, water (streams and lakes) made up 1.4% of the area.
 As of 2007 51.3% of the total municipal area was undergoing some type of construction.
The municipality of Thalwil is located on the Zimmerberg ridge between the western shore of Lake Zurich and the Sihl river. It includes the town of Thalwil, on the eastern slopes of the ridge alongside the lake, and the village of Gattikon, on the westen slopes and the bank of the Sihl. Thalwil borders on the communes of Rüschlikon, Langnau am Albis, Oberrieden, Horgen and (across the lake) Erlenbach.
The municipality has an area of 5.5 km² (2.1 sq mi).  Of this area, 18% is used for agricultural purposes, while 23.8% is forested.  Of the rest of the land, 56.1% is settled (buildings or roads) and the remainder (2.2%) is non-productive (rivers, glaciers or mountains).  In 1996 housing and buildings made up 42.3% of the total area, while transportation infrastructure made up the rest (13.7%).  Of the total unproductive area, water (streams and lakes) made up 1.4% of the area.  As of 2007 51.3% of the total municipal area was undergoing some type of construction.
Thalwil