 The River Diemel, the town's namesake, does not cross through the municipal area, forming only parts of the town limits, and at the same time parts of the boundary between Hesse and North Rhine-Westphalia.One river that does cross through the municipal area, however, is the Orpe, a north-flowing tributary to the Diemel that empties into the larger river at the northern town limits.Diemelstadt lies 12 km north of Bad Arolsen, and 31 km southeast of Paderborn.