| Native Name: | Księstwo wiskie (Polish) Ducatus Wisnensis (Latin) |
| Conventional Long Name: | Duchy of Wizna |
| Era: | High Middle Ages |
| Status: | Fiefdom of the Kingdom of Poland (1345–1351, 1381–1382) Fiefdom of the Kingdom of Poland (1435–1495) Personal union with the Duchy of Płock |
| Government Type: | District principality |
| Life Span: | 1345–1351 1381–1382 1435–1495 |
| Year Start: | 1345 |
| Event Start: | Partition from the Duchy of Rawa |
| Event1: | Incorporation into the Kingdom of Poland |
| Date Event1: | 18 September 1351 |
| Event2: | Partition from Duchy of Masovia |
| Date Event2: | December 1381 |
| Event3: | Pledge to the State of the Teutonic Order |
| Date Event3: | 2 December 1382 |
| Event4: | Partition from the Duchy of Warsaw |
| Date Event4: | 1435 |
| Event End: | Incorporation into the Kingdom of Poland. |
| Year End: | 1495 |
| P1: | Duchy of Rawa |
| P2: | Duchy of Masovia |
| Flag P2: | Chorągiew księcia mazowieckiego Siemowita.svg |
| Border P2: | no |
| P3: | Duchy of Warsaw (district principality)Duchy of Warsaw |
| Flag P3: | Chorągiew Mazowsza.svg |
| Border P3: | no |
| S1: | United Kingdom of Poland |
| Flag S1: | Flag of the Kingdom of Poland.svg |
| Border S1: | no |
| S2: | State of the Teutonic Order |
| Flag S2: | Flag of the State of the Teutonic Order.svg |
| S3: | Crown of the Kingdom of Poland |
| Flag S3: | Flag of the Kingdom of Poland.svg |
| Border S3: | no |
| Religion: | Roman Catholic |
| Flag Border: | no |
| Image Map Caption: | Map of Masovia between 1381 and 1426, with division between lands controlled by Siemowit IV and Janusz I of Warsaw, including Duchy of Wizna. |
| Capital: | Wizna |
| Official Languages: | Polish, Latin |
| Title Leader: | Duke |
| Leader1: | Bolesław III of Płock |
| Year Leader1: | 1345–1351 (first) |
| Year Leader2: | 1381–1382 (second) |
| Leader3: | Władysław I of Płock |
| Year Leader3: | 1435–1495 (third and last) |
Duchy of Wizna was a district principality and a fiefdom within the United Kingdom of Poland, and later the Crown of the Kingdom of Poland. The country was located in Wizna Land with Wizna as its capital and during its existence it remained in the personal union with the Duchy of Płock. It was formed in 1345 from the part of Duchy of Rawa and was ruled by Bolesław III of Płock. On 18 September 1381 it was incorporated into United Kingdom of Poland. It was reestablished in December 1381 from the part of the Duchy of Masovia under Siemowit IV rule. On 2 December 1382 its territory was pledged to the State of the Teutonic Order. It was again re-established in 1435, when it was given to Władysław I of Płock, ruler of the Duchy of Płock, existed until 1495 when it was incorporated into the Crown of the Kingdom of Poland.
Following the death of the ruler of the Duchy of Rawa, Siemowit II of Masovia, on 18 February 1345, Bolesław III of Płock had inherited from him lands of Sochaczew, Gostynin and Wizna. While the first two were incorporated into the Duchy of Płock, the later one was reformed into Duchy of Wizna, remaining in the personal union with Płock. After Bolesław III's death in 1351, on 18 September, the duchy was inherited by the king Casimir III the Great and incorporated into the Kingdom of Poland.[1] In 1370 the territories of the former duchy were transferred to the Duchy of Masovia.
In December 1381, following the death of his father, Siemowit IV had inherited Wizna Land reestablishing the state. On 2 December 1382, he had pledged the lands of the duchy to the State of the Teutonic Order in exchange of 7 000 grzywnas. In November 138 Siemowit IV had longed the period of the pledge in the exchange for 60 000 Prague groschen. In December 1401, he had bought back the Wizna Land from the State of the Teutonic Order which he impliedly pledged to his brother, Janusz I of Warsaw, ruler of the Duchy of Warsaw, for the duration of 9 years. Despite that, Siemowit IV had continued to title himself the Duke of Wizna, while his brother remained from developing the administration and investing in the territory until 1410. The land had remained under Warsaw control until 1435, when it was given to Władysław I of Płock, ruler of the Duchy of Płock and remained in the personal union with the state until 1495 when it was incorporated into the Kingdom of Poland.[2]