The purpose of this study was to evaluate the immunocontraceptive GonaCon™ in reducing fecundity in Eastern gray squirrel (EGS) (Sciurus carolinensis) in urban areas. EGS density on the study area was estimated to be 9 ± (2.89) EGS/ha, based on the Lincoln-Peterson model. There were no significant differences in body weights of treated and control EGS by TS3 (p = 0.40), or testosterone (p = 0.32) and progesterone (p = 0.68) levels. However, there were significant differences in antibody titers between treated and control EGS by TS3 in both males and females active antibodies seen in the treatment group (?2 = 5.656, df = 1, p = 0.017). There were highly significant differences in scrotal size of treated and control males with a reduction in scrotal size being observed in treated males (t= 10.14, df = 8, p = 0.001). There were marked histological changes in treated EGS males and no observable histological changes in treated EGS females. Although there were no serious side effects to the vaccine; 6 EGS developed injection site abscesses. GonaCon™ may be a potential tool to manage EGS overabundance in urban areas, but additional research is needed.