The Asian chestnut gall wasp, Dryocosmus kuriphilus Yasumatsu is an invasive species of global concern that was inadvertently introduced into North America where it induces gall formation on chestnut species including Castanea mollissima Blume, C. crenata Siebold & Zucc., and C. sativa Mill. as well as on the American chestnut, C. dentata (Marshall) Borkh. The gall former was introduced into the United States in the 1970's and since its initial introduction into Georgia, it has been reported to have spread to 13 other states. It has previously been documented as far to the northeast as Connecticut and Massachusetts and as far to the northwest as Michigan. Prior to this study it had been reported in 13 counties within the state of Pennsylvania. The introduction and spread of D. kuriphilus is of particular concern given the intensive efforts to restore American chestnuts into the North American landscape. The purpose of this study was to gain a better understanding of the distribution and spread of the Asian chestnut gall wasp in Eastern Pennsylvania and neighboring states. During the course of this study, specimens of Castanea spp. (Fagaceae) were assessed/monitored for the presence of galls caused by D. kuriphilus at over 100 sites in four states. Herein, galls caused by the Asian chestnut gall wasp are documented, for the first time, on Castanea spp. at several sites in the U.S. states of New Jersey, New York, and Delaware, new state records. Additionally, we report an expansion of the range of the Asian chestnut gall wasp to encompass twenty additional counties within Eastern Pennsylvania. Dispersal of the gall wasps in this study appears to have been influenced by topographical features and wind direction. For further confirmation of identity, we reared D. kuriphilus from galls collected at several sites. These findings establish the range expansion of this gall-forming invasive pest species in the United States to now encompass all of the Mid-Atlantic States.