Casper Platt (June 6, 1892 – September 16, 1965) was a United States federal judge.
Born in Danville, Illinois, Platt received a B.A. from the University of Illinois in 1914 and a J.D. from the University of Chicago Law School in 1916. He was in private practice in Danville, Illinois from 1916 to 1917, and was in the United States Army during World War I, from 1917 to 1918. After the war, he returned to private practice in Danville until 1933, also working as a city attorney for Danville from 1927 to 1928. He was a judge on the Fifth Circuit Court of Illinois from 1933 to 1949.
On September 15, 1949, Platt was nominated by President Harry S Truman to a seat on the United States District Court for the Eastern District of Illinois vacated by Walter C. Lindley. Platt was confirmed by the United States Senate on October 12, 1949, and received his commission on October 13, 1949. He served as chief judge from 1956 until his death in 1965.