There is no record of a last name Merit/Merritt in Johnston county pre-1850.
Also, I don't see any spelling variation for Matthew Jordan or Merit Jordan in Johnston County in any of the pre-1850 census records. These are the only first names that appear: Henry, James, Abner, Dixon, Lewis, Moses, Benjamin, Green Nicholas, Ichabod
As far as Rebecca Jordan goes, you might want to check out this page. I'm not sure that it's who you're looking for, but it might provide a clue.http://digital.ncdcr.gov/cdm/compoundobject/collection/p1501...