We have since found Nathan Johnston listed in the 1850 census as Nashon Johnson with wife Nancy, his age is 60. We have also found evidence of a Nathan Johnston in Madison Co., AL. He purchased supplies at a store. I have not seen the Madison 1830 and 1840 census. A cousin said that there is a Nathan Johnston listed as living in Madison same age with wife and child. We know at one time there were Johnston relatives in the Madison Co., area.
Thanks for the update.