A lot of family papers have been donated to UT...and there is a lot of information, as you stated, but are there official county records there?
Last time I was in Natchez, at the court house, I was told that there are some much older records...THAT DID NOT BURN... but they are kept in a separate vault...that you just have to ASK for them!
ALSO, the Fisk public library in Natchez has a nice collection of old newspaper articles, etc.