Here's what I have on Hiram C. Darwin (1846-1916), husband of Maggie Fox; you probably have all this already, but just in case not, here goes:
1. Parents of Hiram C. Darwin were
William Green Darwin (1803-1851) and Mary Burke (1813-1872)
2.Parents of William Green Darwin were
George Cowan Darwin (1771-1853) and Delilah Harrington (1776-1843); George Cowan Darwin was born in York County, SC, and died in Jackson County, TN
3.Parents of George Cowan Darwin were
James Darwin (1744-ca. 1825) and Mary Cowan (1746-1818)
James Darwin was born in Louisa County, Virginia.
4.Parents of James Darwin were
William Darwin (1707-1786) and Jane (1715-ca.1790), whose maiden name is various given as Wilkinson or Wilkerson, though I have never been able to find a primary source confirming her last name.William Darwin's place of birth is unknown.There are some ingenuous theories connecting him to the family tree of the British scientist Charles R. Darwin, but the evidence for this is not at all good.
I have notes on the families of these folks, if there is anything here of interest