Martha, You asked where William lived after 1870; he was still alive in 1880 in Terrell Co GA.
1880 Terrell Co Ga census page 228D Brightwell, William 76 SC NC NC , Manirvey 46 AL SC SC , Mary 34 GA , Sarah 32 GA , Billie 24 AL , Fronia 18 AL , Lizie 15 AL , Ellen 13 AL , Bobbie 11 AL
Brightwell, Samuel 22 AL SC AL , Elmira 19 AL
NOTE: I think that William's age is exaggerated a little; from earlier census records, he was probably 65-67 years old in 1880.Notice that he says that both parents were born in NORTH Carolina-this agrees with our theory that William's father William (of Barnwell Co SC) was a son of Reynold & Mary Brightwell of Granville/Bute Co NC.
I think that Samuel & Elmira above are the parents of Emmett Brightwell who wrote "the letter".Interestingly Emmett claimed that his father Samuel was a son of William "Thomas" Brightwell's 2nd wife but census records seem to indicate that he was a son of 1st wife Pamela Bush.In 1860 Pamela is still alive and Samuel was born about 1858.