One of the problems in answering is in deciding what would qualify as a Buddhist community, specifically because the word "Buddhist":
- Is a relatively modern and Western invention
- May not mean today what it meant 100 or so years ago (i.e. around the time of the
suspected first Western sangha), and
- Still doesn't have a universally
agreed definition (even taking refuge in the three jewels doesn't
cut it in this context)
With that in mind, you could (given your apparent scholarly bent) bring the Theosophical Society -- 1875 -- into your considerations, as at least being a sangha "precursor", especially given Evan-Wentz's involvement. Clearly it was, by no stretch of the definition, what we'd call "Buddhist" today, but would even the first Buddha and his companions have thought of themselves as "Buddhist" by our contemporary definition? More likely they'd have considered themselves Hindu (although even Hindu is a term which was adopted by late 18th century Europeans to refer to the followers of Indian religions).