Ruth Blair (March 17, 1889 – July 24, 1974) was an American librarian and archivist in the U.S. state of Georgia. She was the first woman state historian of Georgia and the first executive secretary of the Atlanta Historical Society. She helped organize the Society of American Archivists in 1936. Named Atlanta's Woman of the Year in 1955, she has been called "one of the most distinguished archivists in America".

Ruth Blair was born in Douglas County, Georgia, on March 17, 1889, to Hiram Columbus Blair and Nancy Ann Blair (née Mozley). Her father was born in 1836 and served in the Confederate Army; her mother was born in 1851. She had two immediate siblings, Lillian and Hiram Jr. Her father was a successful farmer and briefly represented Douglas County in the Georgia General Assembly. Her father also had been married once before, and thus she had eight half-siblings including Daniel Webster Blair, who was a superior court judge.

After her father's death in 1901, the family moved to Lithia Springs, Georgia. Blair attended Austell High School and Cox College and also was privately tutored for two years. She also took night classes in journalism from Georgia School of Technology professors and correspondence courses in English, history and art from Emory University.

Blair started her first job with the state of Georgia as assistant reference librarian of the Georgia State Library on February 7, 1916. She had no formal training as a librarian, so she learned on the job under the first woman Georgia state librarian, Maud Barker Cobb. She was promoted to legislative librarian in September 1918. She worked at the state library for several years, but she had to resign in late 1919 due to personal and family illnesses. Her mother died in early 1920.

On January 1, 1921, she resumed her career at the newly created Georgia Department of Archives and History as a secretary under Lucian Lamar Knight. Knight described her as his "able assistant" and a "trained investigator with a peculiar gift for organization". Knight arranged for Blair to spend a week at the state archive in Boston in June 1922 to study their methods.

In 1924, as his six-year term was ending, Knight declined re-election by the Georgia Historical Commission due to ill health. Knight "strongly recommended" Blair as his successor. She faced competition from two other candidates: Mildred Lewis Rutherford and educator Charles M. Neel. Blair prevailed by a vote of seven to three. On January 1, 1925 she succeeded Knight as director of the department and as state historian of Georgia, the first woman to do so. She was one of just a few women, including Marie Bankhead Owen and Margaret Cross Norton, who had achieved such a position in the U.S. up to that date. The Atlanta Constitution hailed her appointment as an honor paid to the women of Georgia and harbinger of "the woman's age".

She was responsible for compiling Georgia's Official Register for 1925 through 1931. She also edited and published other publications through the department. However, during her second term the pace of publication slowed due to lack of funds.

The space allotted to the department at the Georgia State Capitol had been limited. Although it had been expanded in 1925, Blair campaigned for a better location for the department and its collections. Through personal connections she secured the donation of the former Amos G. Rhodes home on Peachtree Street to the state for this purpose. The twenty-room stone mansion contained stained glass windows dedicated to the Confederacy. The building was renamed Rhodes Memorial Hall, and the state formally accepted the gift in 1929.