The Province of Nassau (German: Provinz Nassau) was a province of Prussia from 1944-1945.
Although all German states (including Prussia) had been de facto dissolved since 1933, the Nazi government formally dissolved the Prussian province of Hesse-Nassau into two provinces on 1 April 1944, Kurhessen and the province of Nassau.
The name comes from the former Duchy of Nassau (1806-1866), which Prussia annexed following the Austro-Prussian War to form part of the province of Hesse-Nassau.
Following the end of World War II, the province of Nassau fell under American administration. The province of Nassau was dissolved by the occupying US forces on 19 September 1945, forming part of the administrative zone of Greater Hesse. Just over a year later, Greater Hesse became the modern German state of Hesse. Small parts of the province of Nassau also became part of Rhineland-Palatinate.