I remember seeing Belarussian listed as an endangered language, which is unusual for a language with millions of speakers, and a state.
We used to have a Belarussian parish here which was in submission to the Vatican: it's now a Romanian one. The building was a fire station.
There was (is?) a Belarussian Orthodox Church near Ukrainian Village, where the Slavs of all sorts are congregated. It was in a remodeled roller skating rink I think. I don't recall seeing anyone under fifty, but tha was before the fall of communism. I knew a number of Belarussians in the OCA, including our matushka.