I ran across your posting on Rootsweb while searching for other Terhunes. I don't have anything about the Johnsons, but it would appear that Martha Terhune Johnson is a daughter of one of my 2nd great grand-uncles, Adam Terhune of Fleming Co., KY and Nodaway Co., MO. I do have some information about the Terhunes if you are still doing research.
BTW, your post in 2008 was from Sacramento. We just passed through there last week on our way to visit a new grandson in Chico.
E-mail, in case Rootsweb doesn't have my most recent, is firstname.lastname@example.org
La Mesa, CA