“… The Cook County Department of Revenue ('Cook County' or 'Department') is no exception to this trend where in recent years, the Department has increased its audit activity, and much to the chagrin of taxpayers, has taken aggressive positions in the interpretation of its tax ordinances. … The Illinois Constitution grants a home rule unit, which includes a county that has a chief executive officer elected by electors of the county, with authority to exercise any power and perform any function pertaining to its government and affairs, including the power to tax. …”