Hugh Casey was educated at Manual Training High School from 1910 to 1914, graduating at the age of 15. He won a New York State scholarship and entered Brooklyn Polytechnic Institute, where he studied civil engineering. After a year there, he took a competitive examination for the U.S. Military Academy at West Point held by Congressman Daniel J. Griffin, the chairman of the House Committee on Military Affairs, ranking first out of 62 applicants for the appointment. To enter, Casey claimed to be slightly older, adopting his brother's 7 June birthday.