I’m looking for any mention of any French or Belgian-run field hospital/ casualty clearing station/lazarette where wounded African-American soldiers were sent for treatment in WWI. I couldn’t find any online.
Try searching for Base Hospital World War I.
Do you want a segregated hospital where only black soldiers were sent, or do you want hospitals that took all soldiers (including black ones)?
I’m looking for both. Many American-run hospitals from what I gather often turned African-American soldiers away. The French-run stations didn’t, as far as I know. I’m not sure how far the Jim Crow penetrated the British and Canadian stations. So I would be interested in the those stations/hospitals that accepted them as well as those that were segregated.
Black US regiments were attached to the French Army during WWI. So you’d have to figure out what base hospital those regiments’ wounded were being sent to, and go from there. I suspect that they would have been French Army hospitals, and that black US soldiers being sent to US base hospitals would have been pretty uncommon as a result.
This is one of those ways I’m sure Google has gotten worse. I can even see much about French field hospitals in WW1 (where the African American troops would have been treated, as they were under french command and even in french uniforms as described in this article about Henry Johnson), let alone African Americans in French field hospitals. Searching for things like “french field hospitals WW1” brings up a ton of stuff about British field hospitals none about the french, serching for “African Americans french field hospitals ww1” brings up stuff about African Americans in WW1 nothing about field hospitals. 
I’ve seen a few articles about Henry Johnson, all mention that he was wounded, and never received a pension or purple heart as was his due, but none discuss the treatment of his wounds in France.:
The best I could get is this, which doesn’t mention African American troops, but presumably did treat some who were under french command?
Depending on how important this is to you, there is a French Military Hospital Museum, they may may be able to help you (will probably improve your chances if you ask in French however 
)
https://www.cheminsdememoire.gouv.fr/en/revue/musee-du-service-de-sante-des-armees
Thanks griffin1977. This is important to me. I’ve already started searching in French and I’m a little more optimistic about locating specific military field hospitals that way.
One more suggestion. This is the kind of thing that, in my experience, is probably best solved by a book rather than relying on Google. There is good chance an in-depth book on say the Harlem Hellfighters, will likely have some discussion of the medical treatment their injured received.
You could try Google’s newspaper archive. For example, here’s a report of wounded being treated at Fort McHenry in 1919, one of whom was a Harlem Hellfighter.
At least some were treated at Red Cross hospitals in France:
https://catalog.archives.gov/id/45497222
American Military Hospital No. 5, in Auteuil, France seems particularly well documented and a quick googling will reveal several photos including black soldiers. So at least one military hospital appears to have been integrated in WWI, although individual wards may have still been segregated.
BTW my results for this question and your other WWI one about black soldiers were obtained by Googling. Google is still a valuable research resource. Just gotta know how to finesse your search parameters!
Thanks Skywatcher. I’ll look at Fort McHenry.
Very true.
I came across a Moroccan being treated at Auteuil. I’ll look at American Military Hospital No. 5, in AuteuilI. i wasn’t able to open your link. I’ll keep trying.
Good find. Your Google-fu is better than mine.
One thing to note about that photo is they do seem to be wearing French helmets. So the assumption that African American troops under French command would be treated in French field hospitals may not be correct.
Another from the same hospital here. This seems to show African Americans in both French and US uniforms (although it could be French African troops?)