 Diemelsee borders in the north on the town of Marsberg (Hochsauerlandkreis in North Rhine-Westphalia), in the northeast on the town of Bad Arolsen, in the east on the community of Twistetal, in the south on the town of Korbach, in the southwest on the community of Willingen (all in Waldeck-Frankenberg), and in the west on the town of Brilon (Hochsauerlandkreis).The community of Diemelsee came into being as part of municipal reform in 1971 through the voluntary merger of the following 13 centres