When Mary Johns was born in 1722 in Georgetown, South Carolina, her father was John Johns. She married John Smith and they had several children. She died in 1802 in Marion, South Carolina, having lived a long life of 80 years.
Mary Sith Buckholts
Ann Smith Berry
Elizabeth Smith Ely Watson
Sarah Smith Tart
Martha Smith Finklea
Mourning Smith Bryant b. ca 1758 d. 1841, married 1773 Marion County, South Carolina
Cealey Smith Harrelson
Notes for Mary Johns:
Mary Johns was a neighbor or relative of John Smith's previous wife, Jane Ford. They were married within days after the death of Jane.John Smith had two small children at the time.
Will of John Smith IV in Marion Co SC. Mary is given in the will but not her maiden name. Michael Bryant has her name as Polk. Mourning is their child and also James Smith according to his records.  He had her birth year as 1722 of Georgetown, SC and that she died after 1802.
 It refers to her as Mary Johns (the mother of Celia Smith who married Benjamin Harrelson)."
Children of John Smith and Mary Johns are:
1 i. Mourning Smith, born Abt. 1758 in Georgetown District, SC; died 1841 in Marion County, SC; married Jesse Bryan, Sr Abt. 1771 in Georgetown District, SC.
ii. Mary (Polly) Smith6, born 19 September 1750 in Prince Frederick, Winyaw, SC7; died Abt. August 18168; married Major Buckholts; born Abt. 1750.
Notes for Mary (Polly) Smith:
Baptized by Rev. Michael Smith, May 29, 1753.
iii. Sarah Smith9, born 1 December 1751 in Prince Frederick, Winyaw, SC10; married Enos Tart, Sr.; born Abt. 1750; died 18 January 1801 in Gum Swamp, Marion, SC.
Notes for Sarah Smith:
Sarah was baptized May 29., 1753.She married Enos Tart 
Sellers narrative on page 193 says that the daughter of John Smith was the mother of Enos Tart and brothers--not his wife
Sarah was baptized May 29, 1753. 
1802: : Will of John Smith, signed 06/10/1797, was probated on 2/13/1802. Named in the will: wife: Mary, Eldest son: Samuel Smith, other sons: John and James Smith, daus: Mary Buckholts, Ann Berry, Elizabeth Watson, Sarah Tart, Martha Finklea, Mourning Bryant, Cealey Harrelson. Administrators of will: Sons Samuel and John Smith, Witnesses: John Finklea, John Deer. Recorded in Marion Co, SC Will Book 1, pages 16-19. (1)
It may be possible to confirm family relationships with Mary by comparing test results with other carriers of her mitochondrial DNA.
However, there are no known mtDNA test-takers in her direct maternal line.
It is likely that these autosomal DNA test-takers will share DNA with Mary:
Mary Johns was born in what is now called Marion County, SC; therefore, she could not have birth records in a church in Bristol, England. These need to be researched. I do not have an ancestry membership, or I would do it.
The information attached for U.S. Sons of The American Revolution Application is completely different person. This person fought in the Korean Conflict and was from Ohio! Our John Smith fought in The American Revolution and was from South Carolina.
Polk-279 and Johns-319 do not represent the same person because: These are different families who lived in different counties in SC. Also, daughter (Sarah) of Polk-279 was born 1737, daughter (Sarah) of Johns-319 was born 1751.