Dunkelsteinerwald lies in the Mostviertel in Lower Austria. The surface of the market municipality covers 54.19 square kilometers. 46.73 per cent of the surface are wooded.
The municipality includes the catastral districts of Eckartsberg, Gansbach, Gerolding, Geroldinger Wald, Häusling, Heitzing, Hessendorf, Himberg, Hohenwarth, Kicking, Kochholz, Krapfenberg, Lanzing, Lerchfeld, Lottersberg, Mauer bei Melk, Neuhofen, Nölling, Ohnreith, Pfaffing, Thal, Umbach und Ursprung.
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