Serosurveys conducted where West Nile Virus (WNV) caused health impacts were used to construct a model of potential worst case health impacts in a suburban setting. This model addressed two common public perceptions regarding mosquito control activities and WNV disease: it is not a disease of major consequence, and exposed populations quickly become immune. Comparisons to blood bank infection and serious disease incidence data were similar to some of the serosurvey model results. Accounting for theoretical increasing immunity, even over a 20-year period, did not substantially reduce the potential impacts. The model results were approximately an order of magnitude greater than those actually experienced in Suffolk County, NY; differences in mosquito populations and/or the degree of mosquito control between Suffolk County and serosurvey sites seem to be the reason for the differences.