Ternitz is a town and municipality in the district of Neunkirchen, in the Austrian state of Lower Austria. It lies at the confluence of the Sierning stream and the River Schwarza, at the western end of the Steinfeld plain.
The municipality is divided into ten cadastral communities, known in German as Katastralgemeinden: Dunkelstein, Flatz, Holzweg, Mahrersdorf, Pottschach, Putzmannsdorf, Raglitz, Rohrbach am Steinfelde, St. Johann am Steinfelde and Sieding.