I found an 1880 Census in Springport, Cayuga County, New York for the household of Archibald and Mary E. Stewart. With Unis Grinn listed as Archibald's Mother-in-Law. I would love any more information that could be provided.
Also. I suspect Unis may also be listed as Eunice in other records, and that Grinn may also possibly be a misspelling of the original surname. Both Mary E. and Unis are listed as being born in Massachusetts