The Duchy of Sieradz (, ), also known as the Duchy of Siradia, was created based on part of the Duchy of à ÂÃÂczyca in 1263. Duchy of à ÂÃÂczyca was created around 1231 from Province of à ÂÃÂczyca, a part of the Seniorate Province by Konrad I of Masovia.
Ruled by the rivaling Masovian branch of the Piast dynasty. In 1299 Duke Wà Âadysà Âaw I the Elbow-high had to cede Sieradz to King Wenceslaus II of Bohemia, who had also obtained the Seniorate Duchy of Kraków in 1291. Nevertheless, upon the extinction of the Bohemian Pà Âemyslid dynasty in 1306, it was reunited with the Kingdom of Poland as a vassal duchy, and after 1339 incorporated by King Casimir III the Great into the Lands of the Polish Crown as Sieradz Voivodship. Around that time, the term Sieradz Land (Terra Siradiensis, ') begun replacing the older Duchy nomenclature.
The importance of the territory is reflected in the Latin title of Polish kings: nec non terrarum Cracovie, Sandomirrie, Lancicie, Cuyavie, Syradziensis dux.