Subdivisions of the Duchy of Warsaw were based on departments that were headed by prefects. The subsidivions were based on the French model following the erection of the Duchy of Warsaw by Napoleon. The departments were in turn subdivided into traditional Polish powiats (counties). Initially six departments were created out of the province of South Prussia (1793/95 - 1807) in the Kingdom of Prussia. After the 1809 Polish–Austrian War, and the Treaty of Schönbrunn, their number increased to ten (as the Duchy territory was expanded following the annexation of West Galicia). Each department was named after its capital city.
The departments were divided into powiats, and the powiats were divided into urban and rural gminas. Each department was governed by a prefect, while counties were administered by a prefect deputy (Polish: podprefekt). Main cities of the Duchy (Warsaw, Poznan, Kalisz, Torun, Lublin, Kraków and Sandomierz) were administered by mayors (Polish: prezydent), who were nominated by King Frederick Augustus I. The initial six departments were created by a Napoleon’s decree of January 14, 1807. 
In January 1807 the Duchy of Warsaw was divided into the following departments:
Added in 1809, after the Polish - Austrian War (the four departments of former West Galicia were created by a royal decree on February 24, 1810. On April 17, 1810, they were divided into forty counties):
In 1815 the Duchy of Warsaw was divided into Prussian-administered Grand Duchy of Poznań and Russian-controlled Congress Poland. In 1816, the departments of Congress Poland were turned into voivodeships (see Administrative division of Congress Poland).