Donna,
I have looked at the 1870 and 1880 censuses, but they don't help me because I do not descend from any of Wm. Syphax's children. My great grandmother was born to Mary M. Clark in 1854, 8 years before Wm. Syphax's oldest child, Marion, was born. Mary M. Clark was not married at the time and was living in Wisconsin, though she was born in Washington, D.C. in 1833/4 and may have returned there later. After the 1860 census, I cannot find her anywhere, so I'm guessing she probably got married and her last name changed. The Mary M. who married Wm. Syphax was the best fit I could find - identical first name and initial, birth place, race, approximately the same age, and without children born to Wm. Syphax prior to 1860, when my Mary was still in Wisconsin and unmarried. That is why I need to know if Wm. Syphax really married Mary Browne instead of Mary Clark.
Unfortunately, I don't have any information that could help you on Wm. Syphax's grandfather. Also, my Chittendens lived in CT and VT. The only Mary Chittenden I have was born about 100 years too early to have married Charles Syphax.
Please let me know what you have on Mary Browne. Thanks.
Sharon