Hi Doris, I didn't find Alexander in any other Census (checked two Census sources), in FamilySearch or Washington Digital Archives.
I'd contact the Whitman County Genealogical Society, http://www.rootsweb.com/~wawcgs/res.htmhttp://www.rootsweb.com/~wawcgs/res.htm . They do research for $10/hr and they have Whitman County Death Register 18910-1907 and death records extracted from the PUllman Herald Newspaper, 1888-1929.
I'm guessing he died after the 1900 Census because he is not living with the Tady family in the 1910 Census. Successful Searching!