In Jackson Ms at the Archives--there is a book named HUNTING FOR BEARS. I viewed this. IF there was a legal marriage it may be in there listed by groom or bride. I believe the marriage records are online. Everyone did not go to a 'certified' minister to do this. My grgrandparents were not listed but their sons were. Sometimes the cost outweighed the the piece of paper society now decided is necessary, especially if they had been together many years anyway. But could they read what they were making their 'X' on?
I'm sure you have tried just about every website out there and have hit brick walls. If the minister did not turn in the records, it didn't happen. If they went to the court house and paid for a bond and had the Justice of the Peace do so, it may have made the book. I went to the Archives, by doing this the old way so I am only giving you steps I made to view the actually marriage certificates. That piece of paper was not like now. No future benefits.