In October 2012 the Lake County (Illinois) Health Department investigated an outbreak of Salmonella Enteritidis infections among students who attended six different private schools located in Cook (including the City of Chicago) and Lake counties. All six schools received food from the same food service vendor located in Wheeling, Illinois. No other common events or exposures were identified among the ill students. Cases resided in Cook, Lake and Kane counties. Illness onsets ranged from September 14, 2012 to October 10, 2012. One case was hospitalized, four sought care at an emergency room and eight visited a health care provider. Investigators concluded that the most likely source of the outbreak was an infected food handler who through inadequate hygiene may have intermittently contaminated food served at the schools. Suboptimal hygiene was observed during the environmental inspection of the facility that provided the food.