Dillingen is a town in the district of Saarlouis, in Saarland. It has about 20,000 inhabitants and is divided into the three districts Dillingen-city center, Pachten and Diefflen. The city is located on the edge of the Saar-Hunsrück Nature Park at the mouth of the Prims in the Saar and is located about 10 km from the French border. Dillingen is located about 60 km from Luxembourg City and Trier, 50 km from Metz and 30 km from Saarbrücken and is directly adjacent to the urban area of Saarlouis. In terms of population, it is the second largest municipality in the district of Saarlouis. The Dillinger Hütte steelworks is located here.

Dillingen lies to the right of the Saar in the northern part of the Basin of Saarlouis and thus in the Saar-Nahe Basin. The Basin of Saarlouis is bounded on the northwest, north and northeast by the heights of the Buntsandstein. They belong to the eastern edge of the Paris Basin and lead into the basin of the Prims. The Prims coming from the Schwarzwälder Hochwald and emanates above the district of Pachten in the Saar. A few kilometers north of the territorial entity of Pachten the Saar unites with the Nied coming from Lorraine. The alluvial deposits in the basin allow good agricultural use.

Dilingen's Old Castle is a medieval building. Around 1699 it was developed into a Renaissance castle. In 1789 the architect Balthsar Wilhelm Stengel created a grand residential space.

The castle has a yearly arts and crafts market.