The western bean cutworm, Striacosta albicosta (Smith), is a secondary pest of maize (Zea mays L.) and dry beans (Phaseolus vulgaris L.) in the western United States. Recently, this insect has undergone a major territory expansion into the eastern United States and has become a pest throughout much of the Corn Belt. This study was instigated to examine the population genetics of this pest to facilitate control and resistance management, as well as to shed light on the current habitat expansion. S. albicosta individuals were collected from 24 different locations across the traditional and expanded range and amplified fragment length polymorphism analysis was conducted to assess genetic variability. In total, 90 markers were analyzed, encompassing >90% of genetic variation. G_st across all locations was moderately high (G_st = 0.5032). AMOVA analysis revealed that the majority of genetic variation was within locations (54%) and among locations within groups (45%) indicating genetic differentiation of subpopulations. The Mantel test revealed no correlation between geographic and genetic distance (n = 548; r = 0.0045; P = 0.4350). Locations sampled in the eastern United States did not exhibit any reduction in genetic variation in comparison to locations sampled in the western United States, so we conclude that no bottleneck event has occurred with this territory expansion.