| William O. Barnard | |
| State: | Indiana |
| Term Start: | March 4, 1909 |
| Term End: | March 3, 1911 |
| Predecessor: | James Eli Watson |
| Successor: | Finly Hutchinson Gray |
| Birth Name: | William Oscar Barnard |
| Birth Date: | 25 October 1852 |
| Birth Place: | Liberty, Indiana, U.S. |
| Death Place: | New Castle, Indiana, U.S. |
| Restingplace: | Southmound Cemetery |
| Party: | Republican |
William Oscar Barnard (October 25, 1852 – April 8, 1939) was an American lawyer and politician who served one term as a U.S. Representative from Indiana from 1909 to 1911.
Born near Liberty, Indiana, Barnard moved with his parents to Dublin, Indiana, in 1854, to Fayette County in 1856, and to Henry County in 1866.He attended the common schools, and Spiceland Academy, Spiceland, Indiana.
He taught school for five years in Henry and Wayne Counties.He was admitted to the Indiana bar, 1876.He served as prosecuting attorney of the eighteenth and fifty-third judicial circuits from 1887 to 1893.He served as judge of the fifty-third judicial circuit court of Indiana from 1896 to 1902.
Barnard was elected as a Republican to the Sixty-first Congress (March 4, 1909 – March 3, 1911).He was an unsuccessful candidate for reelection to the Sixty-second Congress in 1910.
He resumed the practice of law in New Castle, Indiana.
He died on April 8, 1939, in New Castle, Indiana.He was interred in Southmound Cemetery, New Castle, Indiana.