My family says that we came from Scotland (there's evidently a Margaret that lived in Scotland sometime before the 1700s and somehow she made (or her offspring) made it over here to America).I think she was from around the area of Sterling, Scotland.
I found something that might help you (if you don't know it already that is).Rather than copy the entire posting of what I found, I'll give you the URL I found it at:
Samuel Alexander Sr. b.abt 1657/58 in Raphoe, Donegal, Ulster, Ireland married 1674 in Somerset. Annemessex Mary Taylor b. abt 1650 in somerset co.,Md. died 1733 in Cecil Co., Md.
If that's not your Samuel Alexander, then its an amazing coincidence given his place and date of birth.Perhaps your ancestors (and maybe mine if I can ever confirm who my ancestors are before 1800) migrated to Tennessee from Maryland.In my family's case, I think they migrated to North Carolina before going to Tennessee.Maybe I should look to North Carolina for some records.
Anyway, back to that URL.There is a name and email address for the poster of the message (if you don't know her)...the bad news though is that the post of this message was back in 2000 and I don't know how up-to-date the email address is (maybe you could search for her name elsewhere and see if you can find newer messages).
By the way, I don't know much about William H. (who married Sarah Jane.One of their children (Mary Ellen Alexander) married a Daniel Meyers Alexander and that's about as far as I can get.I can't get a date of birth on William H. though, sorry.