Mumford's father worked for the United Nations from its foundations in 1945 and this was his job while Mumford was growing up. Mumford's mother was American and the family lived on Long Island Sound in the United States, a semi-enclosed arm of the North Atlantic Ocean with the New York- Connecticut shore on the north and Long Island to the south.
Mumford ng ama ay nagtrabaho para sa mga Bansang Nagkakaisa mula sa kanyang komunidad sa 1945 at ito ay ang kanyang trabaho habang Mumford ay lumalaki up. Mumford ng ina ay Amerikano at ang pamilya ay nanirahan sa Long Island Sound sa Estados Unidos, isang semi-bakod braso ng North Atlantic Ocean sa New York-Connecticut baybayin sa north at Long Island sa timog.