William Whitney was born at Conway, Massachusetts, of Puritan stock.
The family were descended from John Whitney of London, who settled at Watertown, Massachusetts, in 1635.
William Whitney's father was Brigadier General James Scollay Whitney; his mother, Laurinda Collins, was a descendant of Plymouth governor William Bradford.
William Whitney had a well known older brother, industrialist Henry Melville Whitney (1839–1923), president of the Metropolitan Steamship Company, founder of the West End Street Railway Company of Boston, and later founder of the Dominion Coal Company and Dominion Iron and Steel Company in Sydney, Nova Scotia on Cape Breton Island.
 His sister Laurinda Collins "Lily" Whitney married Charles T. Barney, who became the president of the Knickerbocker Trust Company.
Another sister, Susan Collins Whitney, married attorney  Henry F. Dimock.

Educated at Williston Seminary, Easthampton, Massachusetts, Whitney was graduated from Yale University in 1863, where he was a member of Skull and Bones, and then studied law at Harvard.
He left in 1864 to study law with Abraham R. Lawrence in New York City, and in 1865 was admitted to the bar.
William Whitney was born at Conway, Massachusetts, of Puritan stock. The family were descended from John Whitney of London, who settled at Watertown, Massachusetts, in 1635. William Whitney's father was Brigadier General James Scollay Whitney; his mother, Laurinda Collins, was a descendant of Plymouth governor William Bradford. William Whitney had a well known older brother, industrialist Henry Melville Whitney (1839–1923), president of the Metropolitan Steamship Company, founder of the West End Street Railway Company of Boston, and later founder of the Dominion Coal Company and Dominion Iron and Steel Company in Sydney, Nova Scotia on Cape Breton Island.  His sister Laurinda Collins "Lily" Whitney married Charles T. Barney, who became the president of the Knickerbocker Trust Company. Another sister, Susan Collins Whitney, married attorney  Henry F. Dimock.
Educated at Williston Seminary, Easthampton, Massachusetts, Whitney was graduated from Yale University in 1863, where he was a member of Skull and Bones, and then studied law at Harvard. He left in 1864 to study law with Abraham R. Lawrence in New York City, and in 1865 was admitted to the bar.
William Collins Whitney