Diemelstadt is a small town in Waldeck-Frankenberg district in Hesse, Germany.

Diemelstadt lies in a small "bay" of Hesse that thrusts into, and is surrounded on three sides by, North Rhine-Westphalia.

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.

The town council's 25 seats are apportioned thus, in accordance with municipal elections held on 26 March 2006: Note: FWG and BL are citizens' coalitions.