William Henry Flack (March 22, 1861 – February 2, 1907) was a Republican member of the U.S. House of Representatives from New York from 1903 to 1907.

He had some family members in Indiana west of downtown Indianapolis in an area known as Flackville.

He served as chairman of the Republican county committee 1898–1902.

Flack was elected as a Republican representative to the United States House of Representatives for the congressional district formed from the 26th District (Essex, New York, Franklin, New York, Clinton, New York and St. Lawrence, New York) to the Fifty-eighth and Fifty-ninth Congresses and served from March 4, 1903, until his death.

[1][2] This article incorporates public domain material from the Biographical Directory of the United States Congress