Dix was born in Newark, New Jersey, to John Edwin and Mary Joy Dix. He attended the Newark Latin School, then Princeton University from which he graduated in 1881 as Latin Salutatorian, and first in his class with highest grade point average awarded to that date (98.5%). While at Princeton he was managing editor of The Lit and was awarded the Boudinot Historical Fellowship and other prizes. In 1884 he graduated from Columbia Law School with highest honors, and subsequently admitted to the bar in New York and New Jersey.