William's birth and marriage are documented, however he disappears after the 1860 census.
Tonight I went looking and finally figured out where he went.
While he appears in the 1860 census (taken 20 June 1860) in Duxbury, it seems he also appears in the census (taken 21 July 1860) of Tatooch (Tatoosh) Island, Clallam County, Washington.
I went on to find the following
The first American settlers at Port Angeles were Angus Johnson, Alexander Sampson (b. abt 1817, Duxbury), Rufus Holmes (b. abt 1814, Duxbury) and William Winsor, although accounts differ as to who arrived first and whether that first arrival came in 1856 or 1857. None brought families -- Sampson was separated from his wife and the others were bachelors. The men staked Donation Land Act claims near the Klallam villages. Sampson located his claim in the cemetery near Tse-whit-zen and residents resisted his intrusion until he worked out an agreement with a local leader that allowed him to build a home on the condition that he not disturb the graves.
A handful of additional settlers arrived over the next few years. In 1859 several of the newer arrivals joined with Sampson, Holmes, and Winsor to form the Cherbourg Land Company to plat a town site and sell lots, despite the fact that by law their donation land claims were only for settlement, not re-sale. The company's name was inspired by Isaac Stevens (1818-1862), former governor of Washington Territory and at the time its Congressional delegate, who foresaw Port Angeles harbor as an important American navy base, dubbing it a "Cherbourg of the Pacific" (Martin, 14). (Cherbourg was a French seaport where Louis XIV established a fortified naval base.)
Cape Flattery Light on Tatoosh Island begins operating on December 28, 1857.
HistoryLink.org Essay 5703
In 1860, William W. Winsor arrived at Tatoosh as the third head keeper. Shortly thereafter, a visitor described trying living conditions at the lighthouse. Rain seeped in under the roof’s shingles, wind drove chimney smoke back into the dwelling, and moss grew on interior walls. This state of affairs lasted until 1875, when authorities repaired the old keepers’ quarters and also built a new, detached living structure.
I thought it might simply be a coincidence that a William W. Winsor, the same age as my own 3rd great-grandfather would be the same one at Tatoosh Island, until I found this court case from the Plymouth County Court of Common Pleas, session begun 7 December 1857:
[16.] Zadock Bradford (Duxbury) v. William W. Winsor (Duxbury). Continued from August term.
Contract, for $90.88 for goods, wares and merchandize was sold and delivered.
Deft. being out of the Commonwealth and no personal service having been made upon him, he was duly notified by the plft.'s publication of an attested copy of the Court order for 3 successive weeks in the Old Colony Memorial.
Default by deft. Judgment for $90.88 and $20.52 costs.
The date is correct for my 3rd great-grandfather to have been the very same William W. Winsor at Tatoosh Island as the light keeper in 1860, and among the first group of white settlers at Port Angeles, Washington.
I have not yet pinpointed a death record, but this evening's discoveries certainly satisfied both the genealogist and Twihard in me.