Depending on where they lived in the county, you might see if maybe they went to Knox or Bell Co's to get married. My ggggrandfather was in Bell Co, then got married in Knox (I never found him to live there) then they settled in Clay Co, so your ancestors could have done the same. Let me know if I can help again.. add a date of when you think they were married or born that way its easier for me to help.. :-) Good luck
Kathy