In the middle of farm country- I’d suggest it was built as a “blockhouse”, to provide safe haven for field workers, trappers, traders, and a few families to flee for safety in case of an Indian attack. Guns and powder could have been stored there in case they were needed
The stockade could have been added later
Just guessing on the function, based on structures mentioned in my western PA family history, one blockhouse (Lochry’s, dating from about 1773) of which still actually exists in Latrobe PA in a preservation area funded by Arnold Palmer in memory of his late wife Winnie
There was no “farm country” back in the day.