Fall armyworm, Spodoptera frugiperda (J.E. Smith) (Lepidoptera: Noctuidae), is a major pest of corn, Zea mays L., and a significant, but more sporadic, pest of cotton, Gossypium hirsutum L., in the Western Hemisphere. Previous studies showed that the cotton infestations primarily involve a fall armyworm subpopulation known as the “corn-strain” for which corn is the preferred host plant. It was suggested that the fall armyworm infesting cotton originated in corn and spread into secondary hosts as their numbers increased. In this study, high positive correlations were found between corn acreage and fall armyworm infestation levels in cotton. These occurred between areas that are either geographically close or along plausible migration pathways. Formulae were derived from scatter plot and linear regression analysis that can predict infestation levels in cotton based on corn acreage. The implications of these results for describing and predicting fall armyworm population movements are discussed.