The 1880 census for Washington county, Maine is not on line. The 1890 federal census burned, so is not available.
Moses Elsemore of Machias, Washington, Maine, who is found in the 1790 Machias census, had 14 children from 1785-1813, 7 sons. Thirteen children married, including all the sons, so lots of Elsemores. It is likely that your William Keene Elsemore is a descendant. I am a descendant of one of Moses's daughters, but don't have details on the Calais Elsemores.
I suggest that you post your Elsemore query to the Washington county Genforum. Also, you might want to join the Roots-L Washington County mail-list and post your query there. http://lists.rootsweb.com/index/usa/ME/http://lists.rootsweb.com/index/usa/ME/