John Clarke Slater was born on December 22, 1900, in Oak Park, Illinois, United States. He was the son of John Rothwell and Katharine Southland (Chapin) Slater. His father was head of the English department at the University of Rochester.
In his boyhood, Slater was very much interested in mathematics and in examining such devices as electrical motors and lamps. His father, whose home library included physics classics like A. A. Michelson’s Light Waves and Their Uses strongly encouraged his son’s scientific bent and in later years would habitually enclose clippings from Scientific American in his letters. Slater’s high school interests also included watercolour painting, architecture, and printing in his attic print shop.