The Illinois Property Tax Code leaves property tax due dates in the discretion of county tax boards, so different due dates may apply in different counties. The default due dates for property taxes are June 1 and September 1. 35 ILCS 200/21-15. However, counties may choose to implement an accelerated billing method with different due dates. 35 ILCS 200/21-30. For example, in Cook County, taxes are due on March 1 and August 1. 35 ILCS 200/21-25Illinois Property Tax System Guide (page 22). Other counties may set different due dates if using an accelerated billing method. 35 ILCS 200/21-20.