I have a new theory regarding your mysterious Mr. Millhone who married Catherine Gallagher.
I just came across this posting in the Cambridge (OH) Jeffersonian dated April 2, 1885:
John Millhone of Nevada, CA is visiting his friends in this county for the third time since his removal to the Golden state thirty-two years ago.He formerly lived between Senecaville and Hartford, and is a brother of Elijah Millhone, of Byesville and Mrs. M.D. Robins of this place.HE gave the Jeffersonian a pleasant call on MOnday and left some nice apples which he grew on his farm adjoining Nevada City.
John I. Millhone was the son of Isaac Millhone and Isabelle Nicholson.HE was born about 1828 in OH. John is listed with his father and his wife Eliza in the 1850 Ohio Census for Guernsey County; the name was misspelled as Milhane.I think that he is the right Mr. Millhone based upon this clue from the newspaper.It places him in Nevada City.Also, the names of the children seem to fit with a daughter named Isabel Mary Millhone and one of the sons names John I. Millhone.