I’m not sure what are “historical records” (but as I assume it defines government documents) and since the capital of Georgia between September-November of 1864 was Milledgeville, Georgia, I’ll assume all “governmental historical records” would have been located there and not in Atlanta. It was in Milledgeville where: “the Federals began destroying valuable books and irreplaceable documents in the state library. One non-participant watched as his blue-clad brothers lay waste to the repository. In his journal, he later noted, ‘I am sure General Sherman will, some day, regret that he permitted this library to be destroyed and plundered’.”
So I’ll say no “Georgia Historical Records” in Atlanta went up in flames for they were in Milledgeville.
I'm giving up on this one.
My searches came up with nothing, not on the pages of the Georgia Archive, neither the National Archive's Atlanta Branch, nor on the Georgia Historical Society website. They all hint to their vast collections of documents from before 1900 - and some promising newspaper sources would not open for Europeans.
While my first thought was that almost all historical records must have been lost to the flames, this amazing webpage proves the contrary - obviously surprisingly many must have survived.
Coming to think of it, maybe I could not find a number of lost documents because they were all miraculously saved?
Yep, I would very much like that, so in the absence of a better number, I'll answer that the percentage of burnt records is zero
Lacking time to research this further, I'll go with what I have found so far. I could not locate any source that mentions a percentage of Georgia's historical record going up in flames when Sherman burned Atlanta on November 12, 1864. An estimated 40% of Atlanta went up in flames, primarily in the business district. But that fact alone wouldn't give a percentage of Georgia's historical records destroyed.
Georgia's historical records would reside at the State Capitol and Archives; during the Civil War, the Georgia State Capitol was in Milledgeville, Georgia, some 100 miles southeast of Atlanta. Milledgeville fell to Sherman on November 22-25; some burning occurred here (primarily parts of the business district, the State Penitentiary , and State Arsenal). Although the State Capitol was vandalized, neither it or the Governor's Mansion were burned. Papers were scattered around in the State Capitol, but little else. All in all, Milledgeville got off light.
A visit to the Georgia Archives website sites that they have records going back to 1733, so that indicates most (if not all) of Georgia's
historical records survived the war.
So, my take is that few (if any) of Georgia's historical records were in Atlanta at the time of the burning on November 12, 1864. If any were, their number would not add up to a percentage point. My answer to the question is: None; 0%.