All you ever wanted to know about levies and assessments (pdf)
This presentation addresses the basics of the budget, levy and property tax cycle.
Your assessment is only one part of the entire property tax cycle. One way to think about property assessment is as the apportionment of the property tax burden on the individual.
Illinois Property Tax Code
To read about the exact legal basis of the property tax cycle.
Truth in Taxation
About Illinois law and requirements concerning budgets, levvys, increases etc.