William Thomas O'Neil (February 7, 1850 – May 5, 1909) was an American politician from New York.

William T. O'Neil was born in Brighton, Franklin County, New York on February 7, 1850.

[1] O'Neil was Supervisor of Waverly in 1881; and a member of the New York State Assembly (Franklin Co.) in 1882, 1883, 1884 and 1885.

He suffered a stroke, and had to be rolled into the Senate chamber in a wheel-chair in January and February 1909.

In March, he became too ill to attend the legislative session, and died on May 5, 1909, at his home in St. Regis Falls.