Hi Lorena, In 1910 Cornleius and Elisabeth were living in Seattle.
However, in 1920 Mrs. Elizabeth Cain was living in Union, Mason Co., WA.
I did find the death record info for Cornelius K. Cain, Age=80, died 3 Oct 1916, Northern States Hospital, Sedro Woolley, Skagit Co., WA. Place of burial=Seattle, WA. Father=Cornelius Cain, father born=USA. Mother=Rebecca Smith, Mother Born=Virginia. No Spouse Name listed. Source: Washington State Digital Archives, www.digitalarchives.wa.gov/ .
I didn't find death info for Elizabeth.
I looked at all of the on-line indexes for cemeteries and didn't find Cornelius or Elizabeth.
Do you have Cornelius's obituary? Sometimes the name of the cemetery will be in the obit.
You can contact Random Acts Genealogical Kindness, www.raogk.org, read guidelines, choose Washington, choose King Co and choose one volunteer.
If that doesn't work out, contact the Washington State Library, www.secstate.wa.gov/library/ask.aspx . They will search the newspaper microfilm for up to 60 minutes and email you with what they do or don't find. Takes about two weeks.
They also might be able to find Elizabeth's death date.
You can also contact the Seattle Genealogical Society, www.rootsweb.ancestry.com/~waseags/ who does research for a reasonable fee.
I also found a family tree on www.ancestry.com which contained Cornelius and Elizabeth. I asked the owner to contact you via your posting. Successful Searching!