Grimmenstein is a town in the district of Neunkirchen, in the Austrian state of Lower Austria. It lies in the eastern part of the country, within the federal province that surrounds Vienna.
The town is one of several municipalities that make up the Neunkirchen district, an administrative area in southern Lower Austria. As a town within this district, it forms part of the broader industrial and commuter region south of Vienna, near the transition between the Vienna Basin and the foothills of the Alps.
Grimmenstein is a small settlement, and its administrative identity is defined chiefly by its status as a municipality within the Neunkirchen district of Lower Austria.