One possibility for the parent of Nancy Thacker and the possible connection of James Johnson on the 1850 census. In the Pike County death records in 1857, there is a DC for ANNA THACKER who died 9 Dec 1857, listed as a widow. Her age is listed as 82 so her birth date should be 1775. Anna's parents are listed as Thomas and Sarah JOHNSON. If this Nancy was a daughter of Anna Johnson Thacker and Unknown Thacker, then the James Johnson could be a nephew from one of her Johnson brothers. (This death record has been confused and used as Amy Tackett wife of William Tackett who was also a daughter of Thomas and Sarah Johnson but is very clearly THACKER)
There is also a marriage record in Pike County for Matilda Thacker who married a Benjamin Sprouse 25 Jan 1824 with permission given by Reuben and Annie, a record for Henry Adkins to marry a Betsy Thacker 3 Feb 1829. On 24 Feb 1829 a record for William Howard to marry a Dorcus Thacker with surity of Reuben Thacker and Joel ADKINS who could be the father or a brother.