Illgau has an area, as of 2006, of 10.9 km² (4.2 sq mi).
Of this area, 62% is used for agricultural purposes, while 31.1% is forested.
Of the rest of the land, 2.9% is settled (buildings or roads) and the remainder (4%) is non-productive (rivers, glaciers or mountains).

It consists of the village sections of Illgau, Vorder Oberberg and Hinter Oberberg as well as scattered farm houses.
All of the farm houses, up to about the 1,300 m (4,300 ft) level are occupied throughout the year.
Illgau has an area, as of 2006, of 10.9 km² (4.2 sq mi). Of this area, 62% is used for agricultural purposes, while 31.1% is forested. Of the rest of the land, 2.9% is settled (buildings or roads) and the remainder (4%) is non-productive (rivers, glaciers or mountains).
It consists of the village sections of Illgau, Vorder Oberberg and Hinter Oberberg as well as scattered farm houses. All of the farm houses, up to about the 1,300 m (4,300 ft) level are occupied throughout the year.
Illgau