What key signatures include a b flat?

ALL FLAT KEY SIGNATURES include a Bb, these are:

F Major/D minor

Bb Major/G minor

Eb Major/C minor

Ab Major/F Minor

Db Major/Bb Minor

Gb Major/Eb Minor

Cb Major/Ab Minor

The reason for this because the order of flats in a key signature is B, E, A, D, G, C, F. From the example above you can see that B-flat (Bb) comes first.