The Duchy of Siewierz was a Silesian 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.

The Duchies of Silesia were the more than twenty divisions of the region of Silesia formed between the 12th and 14th centuries by the breakup of the Duchy of Silesia, then part of the Kingdom of Poland. In 1335, the duchies were ceded to the Kingdom of Bohemia under the Treaty of Trentschin. Thereafter until 1742, Silesia was one of the Bohemian crown lands and lay within the Holy Roman Empire. Most of Silesia was annexed by the King of Prussia under the Treaty of Berlin in 1742. Only the Duchy of Teschen, the Duchy of Troppau and the Duchy of Nysa remained under the control of the Bohemian crown and as such were known as the Duchy of Upper and Lower Silesia until 1918.