Both parents were from leading families, with his father having an estate at Enfield Chase near East Barnet, Hertfordshire which is now in London. George Hadley became high sheriff of Hertfordshire when John was nine years old. John was the second of his parents' six children having an older sister and two younger brothers George and Henry. John was five years older than Henry and three years older than George.
Pareho ang mga magulang ay mula sa mga nangungunang pamilya, sa kanyang ama sa pagkakaroon ng isang ari-arian at Enfield Chase malapit East Barnet, Hertfordshire na ngayon sa London. George Hadley ay naging mataas na serip ng Hertfordshire kapag John ay siyam na taon gulang. John ay ang ikalawang ng kanyang mga magulang 'sa anim na mga bata ang pagkakaroon ng isang mas lumang mga kapatid na babae at dalawang batang kapatid na lalaki at Henry George. John ay limang taon na mas matanda kaysa sa Henry at tatlong taon na mas matanda kaysa sa George.