Percentage Distribution of Population by Religious Communities shows decline in Hindu population from 33.0 percent (1901) to 10.5 percent (1991).
Source:
http://www.bangladeshgov.org/mop/ndb/arpc91_v1/religiou.htm
http://www.bangladeshgov.org/mop/ndb/arpc91_v1/contents.html
Bangladesh- Population census 1991: Religious Composition 1901-1991