In 1821 districts were created in Hessen. They included the districts of Fritzlar, Homberg, Melsungen, and Ziegenhain. In 1932 the districts of Fritzlar and Homberg were merged; in 1974 the three districts of Fritzlar-Homberg, Melsungen, and Ziegenhain were merged into the Schwalm-Eder district.
The two rivers, the Schwalm and the Eder, give the district its name. After they merge close to Felsberg, the Eder enters the Fulda to the north at Edermunde. In the southeast of the district are the hills of the Knüll, where the highest elevation is 634 metres (2,080 ft). To the North are the hills of the Homberger Hochland. The center of the district is largely rural, and is surrounded by the mountains of the Knüll, the Stölzinger Gebirge, and the Kellerwald with the 675 metre-high Wüstegarten mountain.
The soil of weathered Buntsandstein are generally acidic to slightly basic and nutrient-poor. For the most part the land is forested.
In the district of Fritzlar, there are younger outcrops of Upper Buntsandstein, which due to it red colour, is known as the Röt (Engl. Red (beds)). These outcrops consist of clay beds and different kinds of calcareous beds, interbedded with clayey marls.