Which country was created by Napoleon in 1807 from Prussian Polish lands?

The country created by Napoleon in 1807 from Prussian Polish lands was the Duchy of Warsaw.

Napoleon established the duchy through the Treaties of Tilsit after Prussia’s defeat in the War of the Fourth Coalition. It incorporated much of the Polish territory Prussia had gained during the partitions of Poland. The creation revived Polish hopes of restored independence, although Napoleon stopped short of recreating a full Polish kingdom.

The new state was a French client state, formally ruled by Frederick Augustus I of Saxony, who held the title of duke. Its constitution created a parliamentary monarchy with a Sejm, but French military and political interests strongly shaped its government. In 1809, the duchy expanded after Austria’s defeat, acquiring additional former Polish lands under the Treaty of Schönbrunn.

A common mix-up is calling it the Kingdom of Poland. The Duchy of Warsaw remained a separate Napoleonic satellite and lasted until Napoleon’s defeat; the Congress of Vienna dismantled it in 1815, dividing its lands mainly between Russia and Prussia.