Just when/why did Adam come from Williamsburgh County to Old 96?
As the oldest surviving son, we might expect that it would have been Adam rather than Joseph who took over working or managing Archibald's plantation after age began to slow him down (Archibald would have been about 70, give or take a few years when he died) yet this role seems to have gone to second son, Joseph. The first record we find actually mentioning either Adam or Joseph by name is Archibald's estate record so we must "read between the lines". The following tentative time line may help us to construct a reasonable scenario.
1730/31
Adam born (assuming he was born a year or two before his brother Joseph)
1733
His brother Joseph was born
1750
Their mother/siblings may
have been among the 80 who died in an epidemic
ca
1756
Earliest settlement in
immediate area where we later find Adam McKee
1757
Archibald remarries (widowed Mary Witherspoon Wilson)
1762
SC estatblishes "Boonesboro" & encourages settlement there
1762
The Dixons arrive at Charleston & proceed to Boonesboro land which
Adam will acquire
1765
Archibald's second wife dies
1765/74
Archibald remarries again (widowed Elizabeth)
1765/70
Grizzel & Michael are born to Adam
& Jean McKee
1774
John & Prudence Dixon transfer property to Adam & Jean "for
love & affection"
1776
Archibald McKee dies in Williamsburgh Co, names Joseph executor
So as to when Adams went to Old 96, we can be quite sure it was before the birth of their two oldest children -- both named after Jean Dixon McKee's siblings. Their marriage had to be after the Dixon's 1762 arrival but Adam's presence in Old 96 could predate or postdate that of the Dixons. My inclination is to set a range of sometime between 1757 and 1765 with the last three years of that period the most likely but that is merely a guess. .
Why did he go? We can only speculate.
Encyclopedia America tells us that as slaves began to outnumber the white population and an uprising led to the deaths of 21 whites, the government became alarmed and began to induce Europeans to settle in the interior through farm supplies and land grants. "This movement was hastened by the desire of settlers to move away from the malarial swamps of the coastal regions" This malarial concern may have been a major consideration, particularly if we assume it was the cause of the 1750 epidemic and it could have also been a factor in Mary Witherspoon Wilson McKee's death. Considering typical family sizes and the number of Archibald's children surviving to adulthood there might well have been siblings (including an Archibald Jr?) who succumbed to disease during the 1750 epidemic or other early years . Whether or not deaths were that close to home, the homestead was apparantly near a swamp so health could have been a legitimate concern. As to governmental inducements he was already in SC and it does not appear that any land was offered or granted. A farm supplies pot sweetener is a possibility or that he anticipated more incentive than he got.
Might there have been differing concepts on how to farm? Note that Joseph used slave labor but apparantly Adam did not.
Might Archibald's 1757 marriage agreement have played a role? By it there may have been concerns that his stepchildren's rights outweighed those of his natural children. Even in 1810 when Joseph died, references were made to recent estate litigation and four post 1800 claims for Joseph's costs executing Archibald's estate. That was about thirty years after Archibald's death.. Adam left before his father died but may have anticipated problems or been uncomfortable with the new steprelationships..
Or might the spirit of adventure -- new frontiers, new opportunities -- have been the motivating force.
Any of these possibilities or a combination thereof could have played a part in Adam's decision to move across the state.