A new website called County Health Rankings analyzes public health statistics for each county in the US, creating state-by-state reports of the healthiest counties. The website, a joint project of the Robert Wood Johnson Foundation and the University of Wisconsin Population Health Institute, analyzes healh factors (statistics about disease incidence, tobacco use, etc.) and health outcomes (such as life expectancy) to create county-by-county rankings of each state. These rankings are then mapped for each state, using Flash-based Fusion Maps software (not free/open source) so that users can drill down to access county-level data.
"The Opportunity Agenda, with support from the Health Policy Institute at the Joint Center for Political and Economic Studies, commissioned a series of papers examining the effectiveness of web based mapping, and the role it can play in promoting health equity."
The Illinois Department of Public Health has an excellent dataset generator for every Illinois county and MSA across the state. In addition to disease and mortality statistics, you can integrate a wide variety of related demographic and socioeconomic data.