Casimir I of Warsaw

Casimir I of Warsaw (1329/1331 – November/December 1355) was a Piast prince, traditionally the youngest son of Trojden I of Czersk and Maria of Galicia. After Trojden's death in 1341 he ruled Czersk jointly with his brother Siemowit III, and the brothers inherited Rawa in 1345.

In 1349 Casimir received Warsaw as his own duchy, and in 1351 he gained Sochaczew and did homage to Casimir III of Poland. He died unmarried in 1355 and was buried in Płock Cathedral, whereupon Warsaw reverted to the Polish crown.