The Duchy of Warsaw[a] was a feudal district duchy in Masovia, centered on the Warsaw Land.

[1] The state was established in 1310, in the partition of the Duchy of Masovia, with duke Siemowit II of Masovia becoming its first leader.

[1] It existed until 5 November 1370, when, under the rule of duke Siemowit III, duchies of Czersk, Rawa, and Warsaw were unified into the Duchy of Masovia.

[2][3] It was again re-established in June 1381, in the partition of the Duchy of Masovia, with duke Janusz I of Warsaw as its first leader.

[4][5][6] It existed until 1488, when it got incorporated into the Duchy of Czersk.