The Iller (ancient name Ilargus) is a river in Bavaria, Germany. It is a tributary of the Danube, 147 km in length.

The source is located near Oberstdorf in the Allgäu region of the Alps, close to the Austrian border. From there it runs northwards, passing the towns of Sonthofen, Immenstadt, and Kempten. Between Lautrach near Memmingen and Ulm it forms the border between the two German States Bavaria and Baden-Württemberg for about 50 km. The river flows into the Danube in the city of Ulm.

A bicycle route follows the Iller, which is also a popular location for rafting and trekking.

The power of the river is used for the production of hydroelectricity via eight power stations with a total net capacity of 51 MW (1998).

Rivers of Germany | Tributaries of the Danube

Iller | Hilaria | Iller | Hilaria