William Mecklenburg Polk (15 August 1844 – 1918) was an American physician.
He was the son of Leonidas Polk, born at Ashwood, Maury Co., Tenn. He served in the Confederate army under his father during the Civil War, advancing from the rank of cadet to captain. After graduating from the College of Physicians and Surgeons, New York, he settled in the same city, serving as professor of therapeutics and clinical medicine at Bellevue Hospital Medical College (1875–1879), of obstetrics and gynaecology at the University of the City of New York (1879–1898), and subsequently as dean and professor of gynæcology at Cornell University Medical College. He also became connected with many hospitals and dispensaries, and was president of the New York Academy of Medicine in 1910–1914.
He was author of Leonidas Polk, Bishop and General (1893; new edition, two volumes, 1915) and of numerous contributions to medical journals, later reprinted.