Living at the castle until 1594 were various bailiffs (Amtmänner) who represented the joint lords’ (the County of Veldenz, the Margraviate of Baden, Palatinate-Simmern and Palatinate-Zweibrücken) interests.

Margrave Edward Fortunatus was driven out of Baden-Baden in 1594 and sought refuge at the castle, thereby making it a residence once again.

In the course of the Thirty Years' War (1618–1648), the town was occupied by Spaniards, Swedes, Lorrains, Hessians and Frenchmen.

The municipal election held on 7 June 2009 yielded the following results:[3] Kastellaun's mayor is Christian Keimer.

[4] Kastellaun fosters partnerships with the following places: The following are listed buildings or sites in Rhineland-Palatinate’s Directory of Cultural Monuments:[5] On the town's southeastern outskirts is found an indoor swimming pool with an integrated medical rehabilitation centre, and a sport and fitness area.

Ten information stations deal in detail with geology, pedology, root development, climate, weather, life in dead wood, the bark beetle’s voraciousness, natural and artificial forest rejuvenation, mechanized wood harvesting and modern forestry.

Along Kastellaun’s southern outskirts, along the old Hunsrückbahn (railway) right-of-way, runs the Schinderhannes-Radweg (cycle path).

Near Kastellaun lies the former Pydna Missile Base, where each year, an open-air electronic music festival called Nature One is held.

It is among the so-called Schmiedelanstalten (roughly “Swamp Institutions” – named for the wetland area where they were originally found; Julius Reuß was their founder) and is located in a residential neighbourhood between the town centre and the industrial park.

It collaborates with the other institutions in town dedicated to care of the handicapped, namely the Theodor Heuss Schools mentioned above along with their special kindergarten for children with mental disabilities, the workshop and the daytime assistance centre at the Rhein-Mosel-Werkstätten (“Rhine-Moselle Workshops”) and the home of the club Betreutes Wohnen Hunsrück e.V.

The most important buildings and sites and historical events from the castle's and the town's history are described and explained on these tours by expert guides.

Kastellaun lies on the Deutsche Alleenstraße (Germany's longest themed holiday road, featuring many Alleen – tree-lined avenues).

Kastellaun has been home since 20 March 1964 to a Bundeswehr barracks, which houses Command Support Battalion (Führungsunterstützungsbataillon) 282.