m. est. 1712-1715
Facts and Events
John Gass married twice. He married his first wife by about 1715; her name is unknown. He apparently had three children by her, though only two are known by name. In his will John refers to "my three older children". Given that he had only been married to Margaret for six years, it seems likely that this refers to children by a previous marriage. Two of these children by this presumed marriage are believed to be Isabella (b 1716), and Henry Gass (b. 1717), but the identity of the third child is not known.
John and Margaret (and probably his first wife, name unknown) seem to have lived close to the Donegal Presbyterian Meetinghouse, near Mt. Joy, Lancaster, on the east side of the Susuquehannah. According to one source 
James Cunningham was one of the pioneers who settled near Donegal meeting-house in 1723. He took up several hundred acres of land adjoining the glebe land on the north. On the 10th day of March, 1730, he sold to John Gass, whose executors, in 1736, sold to William McClelland and Michael McCleery, who, in 1739, sold to James Kerr, who sold to Andrew Kerr, William Wilson, and William Kerr.
It seems likely that Margarets parents were living in this area at the time of marriage.
Shortly before his death John Gass obtained a Blunston license of land in what is now Cumberland County. 
While the second license ("for the use of the Minister") may be in the Mt. Joy area, near Donegal Meeting House, the other two license' are clearly in what is now Cumberland County.
John died soon after the licenses were issued,. In his will he stipulates that he wished to be buried in the Donegal Cemetery. This may indicate that they couple had recently moved to the Conodoguinet area, and that with death imminent, John sought comfort in being buried in familiar surroundings. Whether this happened or not is not known, as a gravestone for him is not found in the Donegal Meeting House cemetery. Interestingly, soon after John's death Margaret Gass secured a warrant for land on the north side of Conodoguinet Creek. This may be one of the parcels for which John secured a Blunston license. The entry for this warrant in the PA Archives, does not show that the land was ever surveyed.
Benjamin Gass was named exc. in 1734. In his will the elder John Gass directed that his remains "be desently buried in the church yard of Donigall" and that "ye plantation (be left) to my sons." *Donegal Church is located in the present day town of Hershey, Daulphin Co., Pa. At the time of John's death this area was located in Lancaster Co., Pa. No "Gass" is shown as having been a member of Donegal Church. Those I did find with similar spelling are: Joseph and Mary Guess ... Joseph Guest ... The following all have surname Gest: Ann, Benj., Daniel, Deborah, Deborough, Elizabeth, Hannah, Henry, John, Joseph, Margaret, Mary, and Ruth.
It's believed and undoubtedly so, that William Magill was quite possibly the third husband of Margaret Gass. Margaret removed to Virginia sometime after Johns death ... wherein, she and William were married. Thusly, the older children listed for William Magill would be his children and not hers. It's further speculated, because of the unusual request in John Gass' Will, that Margaret may not have been the mother of all of his children and that he feared for her well being after his death.
Chronicles of the Scotch-Irish Settlement in Viginia extracted from the original court records of Augusta Co., 1745-1800. "Abstracts of Wills of Augusta County, Virginia, Augusta County Court ... Will Book Number 1:
Page 202 10th Octorber, 1749. William Magill's will -- Wife, Margaret, and her son, David Gass; sons, James and William, adjoining Charles Campbell; son, John; grandchild, James' son; daughter, Elizabeth. Executors, Robert Cravens, Hugh Campbell. Signed William Magill, Margaret Magill. Teste: Andrew Erwin, Charles Campbell. Proved, 29th November, 1749, when Margaret renounced the will.
(p. 15) An Index to the Will Books and Intestate Records of Lancaster County, Pennsylvania 1729 - 1850 (The following Cowen's can be found in the above described index)