| C. William O'Neill | |
| Order3: | 59th |
| Office3: | Governor of Ohio |
| Term Start3: | January 14, 1957 |
| Term End3: | January 12, 1959 |
| Lieutenant3: | Paul M. Herbert |
| Predecessor3: | John William Brown |
| Successor3: | Michael DiSalle |
| Governor4: | Frank Lausche John William Brown |
| Office4: | 37th Ohio Attorney General |
| Term Start4: | January 8, 1951 |
| Term End4: | January 7, 1957 |
| Predecessor4: | Herbert S. Duffy |
| Successor4: | William B. Saxbe |
| Office2: | Associate Justice of the Ohio Supreme Court |
| Term Start2: | November 30, 1960 |
| Term End2: | April 4, 1970 |
| Predecessor2: | John Weld Peck II |
| Successor2: | Leonard J. Stern |
| Office1: | Chief Justice of the Ohio Supreme Court |
| Term Start1: | April 3, 1970 |
| Term End1: | August 20, 1978 |
| Predecessor1: | Kingsley A. Taft |
| Order5: | 87th |
| Office5: | Speaker of the Ohio House of Representatives |
| Term Start5: | January 6, 1947 |
| Term End5: | January 2, 1949 |
| Successor5: | John F. Cantwell |
| Party: | Republican |
| Birth Date: | 14 February 1916 |
| Birth Place: | Marietta, Ohio, U.S. |
| Death Place: | Columbus, Ohio, U.S. |
| Spouse: | Betty Hewson |
| Alma Mater: | Marietta College, Moritz College of Law |
| Allegiance: |  United States |
| Serviceyears: | 1943–1946 |
| Battles: | World War II |
C. William O'Neill [1] (February 14, 1916 – August 20, 1978) was an American Republican politician, who served as the 59th governor of Ohio.
He was born in Marietta, Ohio. He was the 59th Governor of Ohio. He graduated from both Marietta College (1938) and Ohio State University Moritz College of Law (1942). While at Marietta he joined The Delta Upsilon University.
O'Neill served as a state representative and as Speaker of the House. He was then elected the State Attorney General in 1950, being the youngest person elected to the office at age 34.[1] He served from 1951 to 1957, when he was elected to the governorship. O'Neill served until 1959. He was defeated for re-election due to his support of the controversial proposed "right to work" amendment to the Ohio Constitution. He served on the Ohio Supreme Court from 1960 until his death serving as an associate justice, then chief justice. O'Neill was the only Ohioan to serve in top leadership positions in the legislative, executive and judicial branches of Ohio.[1]
O'Neill was married to Betty Hewson on July 29, 1945, and they had two children. He died August 20, 1978, and his funeral service was at First Community Church in Columbus. He was buried at Oak Grove Cemetery in Marietta.[1]
The O'Neill Building at the Ohio Expo Center and State Fair in Columbus, Ohio, is named in honor of O'Neill. Additionally, The C. William O'Neill Senior Citizens Center in Marietta, Ohio is named in his honor.