On top of this tax, the estate may be subject to the federal estate tax. Illinois imposes its own estate tax separate from the federal estate tax.Illinois's estate tax system is commonly referred to as a "pick up" tax. Property tax is a tax that is based on a property's value. It is sometimes called an "ad valorem" tax, which means "according to value." The exclusion amount is a taxable threshold and not a credit against tax. Illinois has a flat income tax rate of 4.95 percent.