The Duchy of Siewierz was a duchy with its capital in Siewierz. The area was initially part of Lesser Poland, but it was incorporated into Duchy of Silesia established after the death of Duke Bolesław III Wrymouth in 1138 during the times of the fragmentation of Poland. In 1443, the Duchy of Siewierz became a Duchy of Lesser Poland under the control of the Crown of the Kingdom of Poland, which made the Duchy rule by the bishops of Kraków, and here ended Siewierz's history with Silesia, as it became again part of Lesser Poland.
Siewierz was ruled by the Silesian Piasts as part of the Duchy of Bytom under Duke Casimir. In 1312 he granted the town to his youngest son Mieszko, who renounced it in favour of his brother Władysław. In 1337 it was acquired by Casimir I, Duke of Cieszyn, whose scion Wenceslaus I sold it to the Archbishop of Kraków in 1443. Zygmunt Gloger in his book "Historical geography of lands of ancient Poland" ("Geografia historyczna ziem dawnej Polski"), published in 1900, writes that the Duchy of Siewierz belonged to Lesser Poland, after it was bought by the Archbishops of Kraków.
