On maps as of January 2015, Prussia is where Germany is. At its height, the Prussian empire extended up to the Baltic and North seas, from Belgium, the Netherlands, and France to Russia, and to Austria and Hungary.
The Prussian empire eventually became modern-day Germany. After defeating France in 1871, Prussian leadership established Prussia as a world power and unified various states. The Prussians established a German empire, which lasted until World War 1, when the Germans were defeated. The defeat broke up the regions of the Prussian empire into the countries they are known as today including Poland and Germany.