Sophia CORBIN is said to be the daughter of Benjamin & Sarah (SIAS) CORBIN, but Sophia is not mentioned among their children as listed in an 1858 letter by their granddaughter, Keziah — and surely a daughter knows the identity of her mother's siblings.  Nor is there room for Sophia in any of Benjamin & Sarah's census records.  Also, James & Sophia's son, James, says in his 1880 census record that his father was born in VA and his mother in NC.  The former rules out the James from Vermont as his father, while the later rules out any daughter of Benjamin & Sarah (SIAS) CORBIN as his mother, because all of Benjamin & Sarah's children were born in MD. 

There are intermarrying CORBINs and SIASes who moved together from Baltimore/Carroll Co., MD, to Huntingdon Co., PA, and this has led some secondary sources to, apparently, fabricate James being born in the former location and Sophia in the latter, but these assertions are clearly incorrect.  It's obvious that we need to look to the Virginia SIASes and the North Carolina CORBINs to accurately identify this couple.

Do we really know her birthyear?  I have found no primary source for it.

In the 1880 Census, James gives his own birthplace as Virginia, his father's as Virginia, and his mother's as North Carolina, which, if correct, is contrary to all secondary sources regarding his parents' supposed origins.  But as the only primary source I have found, the 1880 census has to trump all secondary sources.

1.  WorldConnect / Ancestry World Trees (online at RootsWeb.com/Ancestry.com).

2.  Descendants of John Sias Sr. by Garey L. Marshall.

3.  Broderbund.  World Family Trees.  Vol. 40, Pedigree #356.  Has Sophia, w/o James SIAS, the d/o Benjamin & Sarah (SIAS) CORBIN, which cannot be correct.

4.  Broderbund.  World Family Trees.  Vol. 1, Pedigree #4903.  Says Sophia CORBIN, w/o James SIAS, was born in "West Minster Co., Maine," but surely "Md" was misread as "Me" somewhere along the line because there is no West Minster or Westminster in Maine and the supposed parents of Sophia lived in Winchester [now Westminster], Baltimore [now Carroll] Co., MD.  However, it appears this location may have been fabricated to support the contention that Sophia was the d/o Benjamin & Sarah (SIAS) CORBIN, which cannot be correct.

5.  U.S. Geological Survey.  Geographic Names Information Service (online database).  "Winchester" in an old name for Westminster, county seat of Carroll [formerly Baltimore] Co., MD.