William Dow is listed in "The Book of Dow" as son of Ebenezer Dow and Hannah page. The 1860 census shows son Orlando living in Newton MA with his sister Clarissa (Dow) Fuller. The Newton entry is under Frank Fuller (his full name was Benjamin Franklin Fuller) and Clarissa is using the name Clara.
Of additional interest is that the dwelling listed just before that has the family from your other query (#1711) on this forum. According to the Dow book, both the line of William and the one of Jeremiah (listed as the father of Daniel b. ca 1835) can be traced to Jeremiah Dow and Martha Goodwin. Jeremiah was a settler of Hollis ME when it was uncleared Forest.
I hope this link between the 2 families is helpful.If you need additional details, please e-mail me directly.