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.