Misc. Notes
That his mother Frances was born in England means he is at least not a full-brother of Timothy Seaman. This William does not seem to appear in the Seaman text by M.T. Seaman, though that deserves a second look.
In 1870, he is listed in Child’s Gazetteer as a farmer in Glenville, along with brother Cornelius S., leasing 90 acres.
77In 1870 census, he is listed as a farmer, as having attended school in the previous year (at 23?), and as an eligible voter. It appears that Mary is his wife.
A William Andrew Seaman is mentioned as the snare drummer for the martial band of Company G, one of ten companies of the 83rd Regiment, National Guard, State of New York, by Percy Van Epps in his article on the brass bands of Glenville. He reports that the regiment formed in 1863 for duty solely in New York State.