Human settlement dates back to the Bronze Age, when Celtic peoples inhabited the region. The Romans established a military camp which grew to become the city of Cambodunum, the present Kempten. It is consequently sometimes claimed that Kempten is the oldest town in Germany.
In medieval times Kempten was a free imperial city, and the surrounding lands became subordinate to the lords of Staufen and the counts of Rothenfels. Both ceased to exist in the beginning of the 19th century, when Napoleon handed these territories over to Bavaria.
The district of Oberallgäu was established in 1972 by merging the former districts of Sonthofen and Kempten.
Oberallgäu is the southernmost district of Germany. "Oberallgäu" literally means "Upper Allgäu". The term Allgäu is applied to the part of the Alps located in Swabia and their northern foothills.
In the very south of the district there are some of the highest mountains of the Allgäu, culminating in the Hochfrottspitze (2649 m). The Iller River (a tributary of the Danube) runs through the district from south to north.