Casimir of Warsaw was born 1325 to Trojden I of Masovia (c1285-1341) and Maria Yuryevna of Halych (c1292-1341) and died 25 November 1355 of unspecified causes. Alfred the Great (849-899)/s, Charlemagne (747-814)/s, Rollo of Normandy (860-932)/s.
Casimir of Warsaw (Polish: Kazimierz c1325-November 26, 1355 ) - Prince of Chersk (1341-1349), Prince of Warsaw (1341-1355) and Prince of Rabbi (1345-1349), the youngest son of Trojden I of Masovia and Maria Yuryevna of Halych. He was a representative of the Mazovian line Piast .
In 1341, after the his father's death, Prince of Czersk and Warsaw Troiden I, Casimir, along with his elder brother Siemowit, took possession of Czersk and Warsaw. In 1345, after the death of his uncle, the prince of Rawa Siemowit II of Masovia, the brothers Casimir and Zemovit took possession of the city of Rawa Mazowiecka.
In 1349, after a new division of his father's principality, Casimir received specific possession of Warsaw , giving Rawa and Czersk to his elder brother Siemowit, took possession of Czersk and Warsaw.
In 1351, after the death of his childless cousin, the prince of Plock and Sochaczew Boleslav III , the brothers Casimir of Warsaw and Siemowit, took possession of Czersk and Warsaw. In 1345, after the death of their uncle, Casimir and the prince of Rabbi Siemowit II of Masovia received joint ownership of Sochaczew. In September of the same year, 1351, the Prince of Warsaw, Boleslav, along with his elder brother, the prince of Plotsk and Czersk Siemowit, took a vassal oath of allegiance to the Polish king Casimir the Great.
Casimir I died between 26 November and 5 December 1355 and was buried at Płock Cathedral. Because he never married or had children, his district of Warsaw as an emptied fief was reverted to King Casimir III; however, he agreed to transfer the entire estate to Siemowit III in exchange of a monetary compensation.
In November 1355, after the death of the childless prince Casimir, his appanage principality was inherited by his elder brother, the prince of Rawa and Czersk, Siemowit, took possession of Czersk and Warsaw.