John Wellborn Root Jr. (July 14, 1887 – October 24, 1963) was a significant United States architect based in Chicago. He was the son of architect John Wellborn Root. As a young man, he graduated from Cornell University and studied architecture at Paris' École nationale supérieure des Beaux-Arts, where he became friends with John Augur Holabird, the son of another famous Chicago architect. Root returned to the States and joined his friend on the architectural staff at Holabird & Roche in 1919. The firm weathered the Depression and Root remained an active partner into old age.