The feast day of St. Casimir is celebrated on March 4th. St. Casimir was a prince of the Kingdom of Poland and Grand Duke of Lithuania who lived in the 15th century. He was known for his piety, devotion to the Eucharist, and his commitment to justice and fairness. St. Casimir is the patron saint of Poland and Lithuania, and his life is an inspiration to all those who seek to live a life of faith and service. On his feast day, we can remember his example and ask for his intercession in our own lives.