The Collaborative International Dictionary of English v.0.48:

Illegality \Il`le*gal"i*ty\, n.; pl. Illegalities. [Cf. F.
   ill['e]galit['e].]
   The quality or condition of being illegal; unlawfulness; as,
   the illegality of trespass or of false imprisonment; also, an
   illegal act.
   [1913 Webster]