OK, here is the original argument I posted for why the reference in The Shadow over Innsmouth to a sanatarium in Canton very likely is the facility currently known as the Pappas Rehabilitation Hospital for Children:
"I have an alternative idea that Lovecraft might have been referring to the Massachusetts Hospital School when he wrote about a sanitarium in Canton. This school was established to help physically disabled children in 1907, and was expanded by a major land purchase in 1920. Thus, I think it could have been mentioned in local papers prior to Lovecraft writing Shadow over Innsmouth in 1931, and so he referenced it to add the the sense of realism at the close of the story.
https://cantonmahistorical.pbworks.com/w/page/34431209/Massachusetts%20Hospital%20School#:~:text=The%20facility%20opened%20in%201907,new%20school%20house%20in%201927.
I’m not sure why he used ‘madhouse’ in one instance in the story and ‘sanitarium’ in two instances. I believe sanitarium was a word used for places where people with long term physical ailments convalesced, and not really a synonym for an asylum. I’ve read sometimes ‘sanitorium’ was used specifically for contagious ailments like tuberculosis, but I’m not sure how specifically the words really were used. Anyway, sanitarium as a place for physical illness makes a bit more sense in that Shadow has less emphasis about madness and more about physical transformations and Lovecraft’s associated anxieties about miscegenation. Also, Lovecraft’s story says it is the ‘poor little cousin’ – I believe meaning a younger person, which again is consistent with the Mass. Hospital School, which was for children. So, by the parlance of the day, there was in fact a facility in Canton MA that might have accurately been called a ‘sanitarium.’ "
The blog owner of Tentaclii helpfully added that the hospital school was called "Industrial School for Crippled and Deformed Children" at the time of Lovecraft writing. Tentaclii makes quite an issue about whether or not Lovecraft could have seen the facility from the train that so famously (locally) crosses the viaduct in Canton, and whether the facility looks suitably 'gothic' for Lovecraft's horror fiction. There isn't really any reason, however, why Lovecraft would ever have needed to see the facility, nor that its appearance be anything notable per se. My thesis is that this very significant land purchase would have been in the newspapers at the time, and that would have been known more broadly to his readership than would the actual experience of seeing the hospital school. Lovecraft added this detail to mix regional authenticity into his fiction. Lovecraft is such a fascinating author I think because of the way he effectively blends genres. He's a regional writer, he's a science fiction writer, a horror writer, etc. In truth, many, maybe at least half of his works are parodies that smack of fan fiction (The Hound is a parody of Poe, Herbet West parody of Frankenstein, Dunwich Horror parodies the Gospels, Whisperer in the Dark parodies Charles Fort, Haunter of the Dark parodies Dracula), and his use of words and sentence structure, although distinctive, isn't regarded generally as great writing. It's the originality and vast scope of his imagination, and the truly effective blending of genres, that I, and I think others, find entertaining and insightful.
So, I think it really was to add that regionalist sense of realism that he mentioned Canton as a location for a sanatarium. Innsmouth is an invented place, and Lovecraft often blended his fictional places like Innsmouth and Arkham with real places. Overall I think the Mass Hospital School is a much better fit than the other possible meanings for his reference to "Canton" in the story, principally because, although Lovecraft at one point refers to it as the "Canton madhouse" he clearly in another line calls it a sanatarium - which was a place for long-term care for physical ailments. Also, the facility was always a place of the care of children, and clearly in Innsmouth the reference is to a child who is in the facility. He may have used the "madhouse" term merely to be pejorative.
That pejorativeness brings me to a potential objection, would Lovecraft really have been so ghoulish as to reference a place dedicated to caring for children in a science fiction horror story? I think he would. Although I admire much of Lovecraft's writing and imagination, he was terribly racist, antisemitic, and eugenicist. He wasn't a "man of his time" - he was notably racist and eugenicist by the standards of his time. So, I don't think he would have had moral objections to using the reference to Canton in this way.
Does any of this matter? I guess not. It's just an interesting (to Lovecraft fans) historical factoid. My thesis could be tested further by someone going to local papers from the time to verify that the hospital school's land purchase or acquisition was in fact in the local papers between 1920 when it occurred and 1930 when Lovecraft wrote The Shadow over Innsmouth. Last point, I've not had direct interaction with the Pappas Rehabilitation Hospital, but I've never heard anything but the most positive things about them. It's an impressive facility whose staff I believe cares deeply for the children in their care. They recently avoided closure by state of Massachusetts, and clearly their care for kids is far more important than historical factoids. I do hope, however, that they might find this blog an interesting, if little known, aspect of the history of their facility that I know is highly thought of within both the local and statewide community.