Because of the increasing incidence of human ehrlichiosis in Wisconsin, we assessed reports of human infections by Ehrlichia chaffeensis and the distribution of its vector, the lone star tick (Amblyomma americanum (L.)). From 2008 through 2015, 158 probable and confirmed human cases of E. chaffeensis infections were reported to the Wisconsin Department of Health Services. Five cases without travel history outside of Wisconsin were confirmed as E. chaffeensis by polymerase chain reaction. Surveillance for the vector occurred from 2008 through 2015 and was based on active and passive methods, including examination of white-tailed deer, collections from live-trapped small mammals, submissions of ticks removed from wild and domestic animals through the Wisconsin Surveillance of Animals for Ticks (SWAT) program, digital or physical submissions by the public to the University of Wisconsin Insect Diagnostic or Medical Entomology laboratories, and active tick dragging. More than 50 lone star ticks (46 adults, 6 nymphs, and 1 larva) were identified. Lone star ticks were more commonly found in south central Wisconsin, particularly in Dane County, where discovery of more than one life stage in a single year indicates possible establishment.