Erasmus was born about 1742, possibly Virginia. (In 1790 there were lots of Nobles in MD, NC & SC). He might have been the son of Erasmus Noble.
He was in South Carolina in 1762. A 1762 mortgage for Abraham Pennington of Berkeley Co, SC lists Erasmus Noble as a witness. (Abraham was likely the brother of Jacob Pennington.)
This 1769 map of South Carolina doesn't show Berkeley County (it seems to be on and off as a state county)
He must have married before 1762 to Mary (b abt 1748), daughter of Jacob Pennington. (Jacob Pennington was in Charleston, SC). Jacob names "daughter Mary Noble" in his will
From “Annals of Tazewell County, VA"
“…in 1764, John Smyth, William Grymes, James Nealey and Israel Christian were appointed to view the roads that led from Vaux’s over the New River on the lands of John Buchanan and likewise by Ingles’ Ferry to the lead mines. And in 1767 James Neely, Philip Love, William Christian and William Bryan were appointed viewers of a road from Vaux’s by Ingles’ Ferry to Peak Creek on the north side of New River. The petitioners were all men of note in the development of the country: Frederick Stern, Isaac Job, Thomas Grayson, John Bell, Henry Skaggs, Joseph Hix, John Draper, George Baker, Joseph Hord, Levy Smith, Erasmus Noble, Samuel Peffer, James Coudon, Edward Vansell, Humphrey Baker, Anthony Bledsoe, James Newell and Alexander Page.” 
Augusta County, VA Records. Vol 1 (477) Mar 18, 1767, Erasmus Noble signed a petition regarding a road “from Vanse’s, by Ingles’s Ferry, to Peak Creek, on north side of New River.” [This is about 25 miles SW of Roanoke, VA, near where the Caseys lived].
Ingles Ferry was at Eagle Bottom
Fort Vause was destroyed in 1756 (French & Indian War)
The Great Road ran from the Yadkin River, NC thru VA to PA 435 miles (probably not suitable for a wagon) 
Erasmus & Mary may have had 2 sons: John and Charles. (It seems strange to me if Erasmus married Mary by 1762, their sons wouldn't be born in 1788 and 1790.) But this descendant of John Noble says he was born in 1788)
There was in the Spartanburg, SC area a Charles Pennington Noble (b 1790) and his older brother, John (b 1788). They appeared in court when they were 14 & 16 years old in 1804 and were allowed to choose their guardians. Mary Nobles left an estate and John and Charles received a small amount of money from the estate when they reached their 21st birthday.
This is another "soft" source for John and Charles:
"John and his brother Charles Pennington Noble were orphaned as children and adopted by two brothers named Brown (Aries and Lewis) - John Noble named a son Bennett Noble - John Nobles' brother was Pennington Noble which leads me to believe his mother was a Pennington"
Erasmus doesn't seem to be anywhere on the 1790 census. By 1790 Mary's sister Charity and her husband, Randolph Casey, had moved to Georgia from SC. Perhaps Erasmus and Mary went with them. Mary probably died sometime in the 1790s, possibly in Georgia.
1792, Mar 12 - Erasmus Nobles got a land grant of "94 acres on branches of Maple Creek, Ninety Six District....surveyed 1784"
This land is about 2-12 miles west of Spartanburg. Maple Creek runs west of Spartanburg.
Perhaps his first wife died after this date.
He married 21-year-old Rebecca Casey (his wife's niece) in about 1796.
Erasmus and Rebecca may have had a baby who was born and died in 1797 (maybe at birth). Then they had Lucinda in 1799 probably after Erasmus died.
His will is file number 1569 in the court of Spartanburg, SC (which makes it look like they weren't in GA). Names his wife (who?), but no children. Lucinda was probably born after he died. He made his will 17 Dec, 1798, and passed away in 1799 in SC. Moses Casey (Rebecca's uncle) was the executor. [Moses' wife, Abigail Pennington, was Mary's sister and Rebecca's aunt].
Here is a copy of the county index online
Does anybody have a copy of this will?
Erasmus was probably about 57 when he died. Rebecca was about 24.
Rebecca took baby Lucinda and went to Tennessee with her parents in 1800. (If her husband had 2 boys, she left them with friends in SC.)
There in Tennessee she met and married William DePriest.
Lucinda named one son James Erasmus for both her father and father-in-law.
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