It was split off the Duchy of Oświęcim, when after eleven years of joint rule the sons of Duke Casimir I in 1445 finally divided the lands among themselves, whereby his eldest son Wenceslaus received the territory around the town of Zator.

[1] After the death of Casimir II in 1490 however both parts of the duchy were reunited, and in 1494 Jan V as the last surviving brother became its sole ruler.

[citation needed] As Jan himself had no heirs, he decided in the same year to sell the duchy to King John I Albert of Poland, under a guarantee that he would remain duke until his death.

At the General sejm of 1564, King Sigismund II Augustus issued privileges of incorporation recognizing both Duchies of Oświęcim and Zator as part of the Polish Crown into the Silesian County of the Kraków Voivodeship, although the Polish kings retained both ducal titles and the name of the Duchy survived in the legal acts (it had however no special privileges).

[citation needed] When the Second Polish Republic was established in 1918, even the ducal title ceased to exist.