Opponitz is a town in the district of Amstetten, in the state of Lower Austria, Austria. It lies in the western part of Lower Austria, within a district whose administrative centre is the town of Amstetten.
The municipality is situated in the foothills of the Austrian Alps, in a landscape of forested slopes and river valleys. The area around Opponitz is drained by the Ybbs river, which flows through the Ybbstal valley toward the Danube. The town's setting reflects the typical character of this part of Lower Austria, where settlements are scattered along valleys between wooded hills.
Opponitz is one of several small municipalities that make up the Amstetten district, a largely rural region of Lower Austria. Like many communities in the area, it is a minor administrative and residential centre rather than a major urban destination.