In 1180 the lands east of the Lech river fell to the Wittelsbach dynasty of Bavaria; the lands on the western bank were acquired about 1315.
The district of Landsberg was established in 1938 as the successor of another entity (Bezirksamt) of the same name. In the administrative reform of 1972 the district received its present shape.
In the final stages of World War II, the German Armaments Ministry and the SS established the Kaufering concentration camp including 11 subcamps in the general area of Landsberg and Kaufering. It was set up as a subcamp of Dachau. At the end of April in 1945, the SS evacuated or destroyed what they could before the Allies arrived.