According to Notable Southern Families, William was a native of Cumberland County, Pennsylvania. He moved to North Carolina before the Revolution, and married Jane Clarke in either Pennsylvania or North Carolina. They had 9 children. The oldest married in 1779, which is the basis for the birth year for William (assuming the son married at 21, and William was 21 when the son was born, puts William's birth about 1737). William lived with his family in Orange County, North Carolina, near Hillsboro.
"Bryan" became "Brien" for one branch of the family over the next generation. Notable Southern Families says of Elisha Brien, a grandson of William and Jane: "One of the sons of William and Jane Clark Bryan had a son, Elisha. Who his father was he failed to tell, but he spelled the name Brien."
William and Jane (Clarke) Bryan's children (as listed in Notable Southern Families) were
Sallie (Bryan) Clark, married William Clark, moved to Logan County, Kentucky (her husband may have been this William Clark: DAR Ancestor #A022769)
Hannah (Bryan) White, married Joseph White
Nancy (Bryan) Scott, married Samuel Scott
John Bryan, had five children, only two known: John and Cynthia
Additional information found clarifies that Elisha's father was John Bryan; three of John's five children moved to Tennessee: Elisha, David, and William (see John Bryan for link to reference for the additional information).
p 57, Notable Southern Families Volume II, Compiled by Zella Armstrong, Member of the Tennessee Historical Commission, published by The Lookout Publishing Company, Chattanooga, Tenn., Dec. 15, 1942. Digitized by Google, and available online through Google Books
Guess for death year based on year of fourth son's marriage (1794), assuming he was married at 21, and adding 5 years for the other five children (1794-21+5)
↑ p 58, Notable Southern Families (see Sources above).
Biography entered by Liz Shifflett, September 23, 2012; updated July 1, 2013
Click the Changes tab for the details of edits by Liz and others.
It may be possible to confirm family relationships with William by comparing test results with other carriers of his Y-chromosome or his mother's mitochondrial DNA.
However, there are no known yDNA or mtDNA test-takers in his direct paternal or maternal line.
It is likely that these autosomal DNA test-takers will share DNA with William:
I'm wondering... Notable Southern Families starts this Bryan line with William from Cumberland County, PA. But... Virginia and North Carolina also have Cumberland counties. I wonder if it was an assumption that he was from the one in Pennsylvania, and what it might have been based on.