What percent of taxes are taken out of your pay check in Illinois?

First, many things that are taken out aren't really taxes and vary from employer to employer. The amount that is taken out varies from person to person, depending on their own personal tax situation, sources of income, deductions and dependents, etc. There are several different prescribed and allowed methods for calculating withholding...projecting an annualization of the income for example. The withholding rate applied then depends on that calculation, and your specific claimed deductions/exemptions, etc. You can control much of it, but if you don't have enough withheld as estimated payments towards your actual tax liability, you would be subject to penalties, interest charges, and even having the right to decide it restricted. You should talk to the payroll area and they can tell you exactly how and why it is calculated as it is.