| Mary Estill Buchanan | |
| Office: | 30th Secretary of State of Colorado |
| Governor: | John D. Vanderhoof Richard Lamm |
| Term Start: | March 21, 1974 |
| Term End: | January 11, 1983 |
| Predecessor: | Bryon Anderson |
| Successor: | Natalie Meyer |
| Birth Date: | 15 November 1934 |
| Birth Place: | San Francisco, California, U.S. |
| Party: | Republican |
| Education: | Wellesley College (BA) Harvard University (MBA) |
Mary Estill Buchanan (born November 15, 1934) is an American politician who served as the Secretary of State of Colorado from 1974 to 1983.[1] [2] She was the Republican nominee for U.S. Senate in 1980, but was narrowly defeated by incumbent Gary Hart.