The Iller is a river in Bavaria, Germany. It is a tributary of the Danube and 147.0 km in length.
The source is located in the Alps of the Allg? region, close to the Austrian border. From here it runs northwards, passing the cities of Immenstadt and Kempten. Between Memmingen and Ulm it forms the border of Bavaria and Baden-W?ttemberg for about 50 km. The river enters the Danube in the city of Ulm.