John Casimir

John Casimir may refer to:
 * John II Casimir of Poland (1609–1672)
 * Johann Casimir of Simmern (1543–1592)
 * John Casimir, Duke of Saxe-Coburg (1564–1633)
 * John Casimir (clarinetist) (1898–1963)
 * John Casimir, Count Palatine of Kleeburg (1589–1652), father of Karl X Gustav of Sweden
 * John Casimir Ehrnrooth, Finnish soldier
 * John Casimir Zichy Woinarski, Australian ornithologist