Dillenburg, officially Oranienstadt Dillenburg, is a town in Hesse's Gießen region in Germany. The town was formerly the seat of the old Dillkreis district, which is now part of the Lahn-Dill-Kreis.

The town lies on the German-Dutch holiday road called the Orange Route, joining towns, cities and regions associated with the House of Orange-Nassau, as well as on the German Timber-Frame Road and the Rothaarsteig hiking trail.

Dillenburg lies on the eastern edge of the Westerwald range in the narrow valley of the river Dill, which flows from Hesse-Westphalia border to Wetzlar, emptying into the Lahn.

Culture and sightseeing:

• Wilhelmsturm (tower) with the Orange-Nassau Museum
• "Villa Grün" museum of economic history
• The "Casemates", old defensive structures.
• Hessisches Landgestüt (Hessian State Stud Farm) with coach museum in the Orangery. "Living Museum" about the horse.
• The "Casemates", old defensive structures.from the 16th century
• The Evangelische Town Church from 1491
• The Dillturm (tower) from 1597
• The old rectory from 1531-1533
• The Untertor (Lower Gate) from 1344 (alterations in 1594 and 1737)
• Manderbach Church
• Donsbach Wildlife Park
• Brineworks and healing spring, Eibach