The old Newcomb genealogies list Capt. Philetus Newcomb, the son of Doctor Luther Newcomb and Anna Salisbury (out of wedlock). He married Rhoda Hayes in 1820, and they had several children prior to his death in 1837.
I now believe his correct name was Miletus, not Philetus.
The headstone in Gaffield Cemetery says Miletus.
He had a son named Miletus, and that son also had a son named Miletus.
There is a military service card from the "Register of officers terminated prior to Jan. 1858" listing a Capt. Miletus Newcomb.
The 1830 U.S. Census for Wilmington NY lists a Miletus Newcomb with five young children and an adult female in his houshold.
There is a birth record for Miletus Salisbury, born December 28, 1798, in Brattleboro VT, mother's name Anna, father's name Newcomb Salisbury, father's occupation doctor.
My conclusion is that his name was Miletus. The confusion seems to have come about because Miletus and Philetus rhyme, and because there was a Philetus Newcomb of about the same age who also married a woman named Rhoda. All those similar names can be confusing.