In 1888, Yale conferred upon him the honorary degree of LL.D.

Whitney joined Charles T. Barney, Henry F. Dimock, W.E.D. Stokes, Francis W. Jenks, and others in forming the New York Loan and Improvement Company in 1890. 
This concern developed the Washington Heights section of New York City. 
Barney was president of the company when he died in 1907, three years after Whitney.  In opposition to Tammany, Whitney was instrumental in bringing about the third nomination of Cleveland in 1892, and took an influential part in the ensuing presidential campaign.

Whitney joined his brother Henry in organizing the Dominion Coal Company Ltd. in 1893, and the Dominion Iron and Steel Company Ltd. in 1899, to exploit the mineral resources of the Sydney district of Cape Breton Island. Other earlyinvestors included Henry F. Dimock, Almeric H. Paget and Charles T. Barney.  In the next general election, in 1896, disapproving of the "free-silver" agitation, Whitney refused to support his party's candidate, William Jennings Bryan.

Thoroughbred horse racing
William Whitney was also a major investor in thoroughbred horse racing, hiring the best trainers, buying the best horses, and engaging the services of the best jockey of the day. He established Westbury Stable with a string of thoroughbred race horses, competing against the successful stable of business associate James R. Keene. At his vast summer estate near Old Westbury on Long Island, Whitney built an  stable with 84 box stalls and an adjoining mile-long training track. Around the start of the 20th century, in the United States his horses were