  We construct the characters for the highest weight representations of the 3d
Bondi-Metzner-Sachs (BMS$_3$) algebra. We then use these to construct the
partition function and show how to use BMS modular transformations to obtain a
density of primary states. The entropy thus obtained accounts for the principle
part of the entropy obtained from the BMS-Cardy formula. This suggests that BMS
primaries capture most of the entropy of Flat Space Cosmologies, which are the
flatspace analogues of BTZ black holes in AdS$_3$. We reproduce our character
formula by looking at singular limits from 2d CFT characters and find that our
answers are identical to the characters obtained for the very different induced
representations. We offer an algebraic explanation to this arising from a (to
the best of our knowledge) novel automorphism in the parent 2d CFT.
