In Illinois, when an employee is terminated, the employer is required to make full payment of all amounts due to the employee at the next scheduled payroll.  This may include compensation for unused vacation days, but typically does not include compensation for unused sick days or holidays (unless otherwise contracted).  

If the employer fails to timely pay the full amount due to the employee, the Illinois Wage Payment and Collection Act provides that the employee is entitled to recover:

• The full amount of pay due and owing; 
• Attorney fees and court costs expended in collecting such amount; and 
• A penalty equaling 2% of the unpaid wages for each month that the wages remain unpaid.  

You can find an excellent FAQ regarding the Wage Payment and Collection Act here, at the Illinois Department of Labor's website.