[2] Ruled by the rivaling Masovian branch of the Piast dynasty.

In 1299 Duke Władysław 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 Přemyslid 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, ziemia sieradzka) 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.