William L. Sweet (October 25, 1850, in Waterloo, Seneca County, New York – August 4, 1931, in Waterloo, Seneca Co., NY) was an American politician from New York.
He was the son of Abram Sweet and Charlotte (Cook) Sweet. He graduated from Cazenovia Seminary in 1867. Then he became a merchant, trading in produce, grains and flour. On June 4, 1874, he married Mary Asenath Cook (1852–1937), and they had several children, among them Cdr. George Cook Sweet NC (1877–1953).
Sweet was President of the Board of Education of Waterloo in 1884; President of the Village of Waterloo in 1885 and 1886; a member of the New York State Assembly (Seneca Co.) in 1887; and a member of the New York State Senate (26th D.) in 1888 and 1889.