Dierdorf () is a town in the district of Neuwied, in Rhineland-Palatinate, Germany. It is situated in the Westerwald, approx. 20 km northeast of Neuwied, and 20 km north of Koblenz.
From the end of the 17th century until 1824, it was the seat of the counts and princes of Wied-Runkel, who resided at Dierdorf Castle, which was demolished in 1902.
Dierdorf is the seat of the Verbandsgemeinde ("collective municipality") Dierdorf.
The elections in May 2014 showed the following results.
Dierdorf is the sister city of Fountain Hills (USA), Courtisols (France) and Krotoszyn (Poland).
Dierdorf had a train station on the Engers-Au railway line, the section from Siershahn to Altenkirchen nowadays is only served by fright trains, nearest train station nowadays is Siershahn.