John Sweat of Chester Co., SC is in the 1810 census age 26-45 and in the 1820 census in the 45+ column.
The John Sweat whose will was written in 1816 and proved in 1818 was in Fairfield Co. He was probably born about 1740 (according to "Sweat Families of the South" by Erbon Wise, p. 24).Since he died in 1818, he would not be the John Sweat in Chester Co.
Marion Co. is quite a distance from Chester and Fairfield Counties and I have never thought that the John Sweet found there had any connection with the John in Fairfield or the one in Chester, but I still don't know any history for them.
I do know that an Anthony Sweat in Sumner Co., TN married Hannah Groom in 1804.I have not found anything to say that this Anthony Sweat came from anywhere other than NC like his neighbors.