loeb was born to a jewish family on november 11, 1902, in st. louis, missouri, the son of adeline (née moses) and carl m. loeb. his father was an immigrant from germany who made a fortune after gaining control of the american metal company (founded by berthold hochschild and jacob longeloth) jacob longeloth was his father's mentor hence his son's middle name. his mother was the daughter of alabama banker, alfred huger moses. he had three siblings: carl m. loeb, jr., henry a. loeb and margaret loeb kempner. loeb attended dartmouth college and then transferred to harvard college where he graduated in 1924.