Most sources note that Thomas was either born in Virginia or Ireland. Thomas was most likely born in Virginia, however we cannot yet rule out Ireland as a possibility.

Thomas may have been enumerated in Anna Walsh's household in the 1840 census. If Anna is Honora, Thomas would have fell in the "Male - 5 & under 10" age bracket at about 6 years old.

Thomas was living in his oldest brother's household in the 28th District (Harpers Ferry) of Jefferson County, West Virginia.

Thomas bought a "spotted hog" for $5.25 on nine months credit at the estate sale of William Flanagan, held by son and estate administrator James Flanagan. The first choice "fat" hog sold to William Osbourne for $13.75. Osbourne also bought the second and third choice "fat" hogs for $11.12 1/2 and $9.12 1/2 respectively. By looking at the appraisal of the estate, it is likely that the hog Thomas purchased was the Flanagan's brood sow.

Thomas married Annie Gertrude Murphy in 1859 at St. Peters Catholic Church in Harpers Ferry. Annie was likely pregnant with their first son, John Martin, during their marriage.

Annie gave birth to Thomas' first born child, John Martin Welsh, in Oak Grove (Bakerton).

Thomas was living in the 28th district with his new wife Annie and son John. His nephew, Michael, a young Elizabeth Slavin, and boarder William Jackson were also present. Thomas' occupation is listed as laborer.

On a Tuesday, Thomas' second child and son, Thomas Buchanon Welsh, was born. Thomas named the little boy after himself.

Thomas' third child and son, Patrick Henry Welsh, was born on a Tuesday. Patrick was likely named after Thomas' father.

On a Wednesday, Thomas' fourth child, but first-born daughter, Nora Frances Welsh, was born. Thomas' likely named his daughter after his mother, Honora.

On a Monday, Thomas' and Annie's fifth child was born ten years after their marriage. Their daughter took her mother's name, Annie Gertrude.

Thomas is enumerated in the 1870 Federal Census alongside his small family near Bolivar (likely the Oak Grove area). Thomas' household neighbors the Flanagan's households. His occupation is listed as being 'work in stone quarry'. While Thomas is listed as being born in West Virginia, the parents of both Thomas and Annie are listed as being foreign born. Thomas notes that his son, John, attended school within the year, and he can read but cannot write. Thomas also lists himself as a citizen of the United States.

On a Saturday, Annie gave birth to a daughter, whom they named Mary E.

Thomas' lost his newborn daughter, Mary, early in 1871. Little information has been uncovered about her death. It appears as if the couple had Mary cremated, later to be buried with her younger brother and wife.

Thomas' brother, James, passed away on a Monday from pneumonia. Thomas is listed as the informant on his brother's death certificate.

William Franklin Welsh was born on Wednesday to Thomas and Annie.

Sometime during the year of 1874, the couple's was blessed with another daughter, whom they named Catherine Irene.

Thomas succumbed to pneumonia on March 11, 1875. His employer, Les Sprow, was the informant for his death record. According to the 1870 census, George Sprow was the superintendent for the stone quarry at Bakerton. Thomas was buried in St. Peters Cemetery alongside his oldest brother, Martin.