Written history in the area began about 800 AD, when the Danish Viking settlement of Haithabu was founded. Later the neighbouring city of Schleswig took the place of Haithabu and became a powerful town in the 11th century. It later lost its power to Lübeck.
The district was established in 1974 by merging the former districts of Flensburg-Land and Schleswig. Due to the proximity of Denmark and the regional history there is a large percentage of Danish inhabitants.
The countryside is generally plain. The Schlei, a firth of the Baltic Sea, is the southern border of this district. All the land north of the Schlei and south of Flensburg is called the peninsula of Angeln. Angeln was the ancient home of the Germanic people known as the Angles, who migrated to England in the early Middle Ages.