Warsaw Department (Polish: Departament warszawski) was a unit of administrative division and local government in the Duchy of Warsaw in years 1806–1815. Its capital was Warsaw. Administrative division: 10 counties Błonie County Brzezin County Czersk County Gostynin County Łęczyca County Orłów County Rawa Mazowiecka County Sochaczew County Warszawa County Zgiersk County Siennick County (1810) Stanisławow County (1810) In 1815 it was transformed into Masovian Voivodeship. References Jacek Arkadiusz Goclon, Polska na królu pruskim zdobyta, Wydawnictwo Uniwersytetu Wrocławskiego, Wrocław 2002. Mieczysław Bandurka, Zmiany administracyjne i terytorialne ziem województwa łódzkiego w XIX i XX wieku, NDAP, UW w Łodzi, AP w Łodzi, Łódź 1995. Departments of the Duchy of Warsaw History of Warsaw