We are getting off the Stitt track here, but...My father James X McIlwain was born 1917. His great-grandfather James Xenophon was born 1831. I am aware of at least three Johns: 1)Father of James Xenophon, born 1798, foreign-born; 2) Brother of James Xenophon, born about 1836. Served in the PA 78th during the Civil War; 3)Son of James Xenophon, born about 1873, John K. McIlwain.
Father John McIlwain died in 1837. His wife Jane remarried, to a John T. Smith.
The John McIlwain who served in the Civil War seems to have died young, but may have married and produced a couple of children.
James Xenophon had several sons in addition to John K. The eldest was Xenophon Whitlinger (b.1859). There was also Harry, Charles, and James (called Lawrence?). Also two daughters: Georgiana (Georgia?) and Margaret (married McKinstry).
Was your GGGrandmother (married to John McIlwain) "Catherine Porter?"
Do you know anything about a DANIEL MCILWAIN, born about 1801?