I came across this Q/A
Mes parents vivent ________ Languedoc-Roussillon
The only answer accepted is dans le Languedoc-Roussillon yet I have seen numerous instances en Languedoc-Roussillon cited in many august sources.
I will reference only one from INSEE:
"La pauvreté en Languedoc-Roussillon" - www.insee.fr/fr/statistiques/1894450
Is INSEE wrong?
Tom