John Forsythe and sister Mary Ann Forsythe are the only two children of Thomas and Elizabeth Forsythe. Brother and sister, John and Mary Ann, and parents, Thomas and Elizabeth, all moved to Iowa in the early 1850s - but at slightly different times. To the north, in Wapello County, Iowa there would be a Forsyth (no e) family. There is no known relationship except some inter-marriage. One daughter, Eliza, married Joseph Morrison. They had one child, John Thomas who married John's daughter Nancy Rebeca. Also, a brother of Eliza, William, married John's sister Mary Ann. All of these individuals lived in the Westmoreland County, Pennsylvania area. It is not clear what reason was for the chain of migration to Iowa, but the Glassburner family, who also lived in Westmoreland County, started by deciding to move to Marion Township, Davis County in 1847. In 1851, the Forsyth family moved to Richland Township in Wapello County, Iowa - with the exception of 3 children including William and Mary Ann Forsyth and Joseph and Eliza Forsyth Morrison. In 1853 William and Joseph moved to Wapello County for William to be near his ailing father. In 1854 their wives, Mary Ann and Eliza, joined them. In 1855 John and wife Mary Ann and their family, along with his parents Thomas and Elizabeth, moved to Davis County and William and Mary Ann moved nearby from Wapello County. Thomas and John and families stayed together in this spot near Ash Grove for the remainder of their lives.

It is most likely that John was born in Allegheny County, not Fayette County. Thomas Jr. and Elizabeth were married there in 1811. Thomas served there in the militia in the War of 1812 in the latter part of 1812. And Thomas Jr. did not reappear in Fayette County tax lists until 1817.