Hi Mary, assuming that Benton died in Whatcom County, I'd contact the Whatcom Genealogy Society, http://members.aol.com/whatcom59/wgs.htmlhttp://members.aol.com/whatcom59/wgs.html . They should have the WA Death Index microfilm and can look up his death date for a reasonable fee. They also have a lot of other resources.
It's odd though that he doesn't appear in the 1900 Census. However, Blaine is so close to British Columbia and people moved back and forth across the border. Check out British Columbia records too. Successful Searching!