Alexander Duncan Ellis
when applying for a passport in November 1921, he said he lived in North Chelmsford and was going to England for four months to visit his mother. North Chelmsford is in Middlesex County
https://www.familysearch.org/ark:/61903/1:1:QV5Y-764J-----------
His son Alexander is buried in Central Cemetery, Beverly, Essex County.
https://www.findagrave.com/memorial/97766429/alexander-ellisThat is one place you could look.
I didn't see wife Emily, daughter Emily, or son Thomas at findagrave.
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His death might be registered in Chelmsford and maybe Lowell. I have a feeling the death would be registered in Massachusetts even if he died in England. Did he, while visiting his mother?:
Alexander D Ellis Chelmsford 1922 Vol 13 page 241
Alexander D Ellis Lowell 1922 Vol 41 page 172
found at ancestry. it doesn't look like the image of the record itself is online yet
If they are not the same man, then Chelmsford is the more likely, since he lived there in 1921.
I don't remember if a Massachusetts death record lists the place of burial. Deal with the town first, they are usually cheaper than the state. Unless the record has gone to the state archives, which you can find out by asking them.
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There should be an obituary in a local paper. Chelmsford library would probably be helpful.