The Federal Communications Commission (FCC) Phase II enhanced 911 (E-911) requirements have motivated increased interest in the challenge of localizing mobile sources in urban environments. The FCC E-911 Phase-II requires wireless carriers to provide the location of a 911 caller with accuracy of 100 meters in 67% of cases and 300 meters in 95% of cases. This work proposes an information theoretic bound on mobile station (MS) localization performance in urban environments that provides an alternative criterion for the MS localization performance evaluation. The proposed lower bound provides necessary, but not sufficient conditions for achieving arbitrary small probability of the localization error. The MS localization problem is modeled in the framework of communication via channels where the source location is modeled as a transmitted message which is encoded by the propagation conditions. The bound is evaluated for variety of propagation conditions predicted by a recently proposed statistical model of urban propagation conditions. The bound is demonstrated to apply to urban scenes of interest, and the sensitivity of the bound to changes in propagation conditions is discussed.