Tax Policy Center studied residential property tax rates;  the three highest in Illinois are DuPage, Lake and Cook.

http://politics.rebootillinois.com/2014/02/18/editors-picks/brendanbond/counties-highest-property-taxes/438/#.UxDDjvmwJdw?utm_source=twitter&utm_medium=social&utm_campaign=rebootillinois3/16/2014