"My" Edmund Gilliam of Orange County, NC did have a wife Sarah; however, her last name was Magee/McGee not Clark. She was the daughter of Ralph Magee and Ann. She is mentioned in her father's Will.
I know that you believe that "my" Edmund Gilliam is not "your" Edmund Gillum/Gilham, but if one looks at the census records there was only one Edmund living in Orange at the time. And here in NC the name "Gilliam" is pronounced as the two-syllable "Gillum." In fact, in records it is spelt a dozen different ways including Gilham and Gillham. [In one Orange County deed Edmund's name is spelt Gilin!]
I believe your Elizabeth who married Samuel C. Lee is not related to the Gilliams of Orange County, NC, but rather another line, possibly one out of PA or central VA. I am also curious about the birth date and place you give for Elizabeth. The first permanent American settlement in Ohio was at Marietta in 1788. Several years after the birth of your Elizabeth in Ohio, so I question that Elizabeth was born October 4, 1780 in Wilmington, Highland, Ohio. (Ia stickler for details since I teach history.)
Anyway . . . here is the Will of Edmund Gilliam. Edmund Gilliam, 11 Aug 1810 N.C. State Archives under Orange County Records.
Edmund GILLIAM In the name of God Amen. I Edmund GILLIAM of Orange County and State of North Carolina being weak in Body but of sound and perfect mind and memory blessed be to god for the same do make and publish this my Last will and in manner and form following. That is to say first I give to my Son Edmund GILLIAM one Negro man named Stephen and one cow and calf and set of Smith Tools. I likewise give my Sons Charles and Burwell the tract of land that Charles lives on as it was divided between them lying on the south west side of Haw River. I give to my son David the land I live on, on the north east side of the River. I likewise give my daughters Sarah HURBIN one Feather bed and furniture. I likewise give to my well beloved wife Sarah GILLIAM all the rest of my property and at her death the property that is willed to her to be Equally Divided between my four daughters namely Susannah SMOTHERS Sarah HURBIN Mary BRACKIN and Elizabeth STALCUP to them and their heirs forever and I make and appoint my Son Edmund GILLIAM Executor desiring my sd. Son to Take on him the charge and Trouble thereof and to see the same performed according to my true intent and meaning and Lastly Thereby Revoke all former will or wills by me made and Declare this only to be my Last Will and Testament in Witness whereof The said Edmund GILLIAM hath hereunto set my hand and seal in the presents of Thomas BRADFORD Jurat and David BRADFORD Sr. August ye 11th 1810. Signed by his mark: Edmund GILLIAM Burwell GILLIAM qualified
If you do find that your Gilliams/Gilhams trace back to VA or NC I will be glad to help. I have been tracing VA and NC Gilliams for quite some time and have a rather large Gilliam database.