Ill. Const. art. IX, § 5

(a) The General Assembly by law may classify personal property for purposes of taxation by valuation, abolish such taxes on any or all classes and authorize the levy of taxes in lieu of the taxation of personal property by valuation.

(b) Any ad valorem personal property tax abolished on or before the effective date of this Constitution shall not be reinstated.

(c) On or before January 1, 1979, the General Assembly by law shall abolish all ad valorem personal property taxes and concurrently therewith and thereafter shall replace all revenue lost by units of local government and school districts as a result of the abolition of ad valorem personal property taxes subsequent to January 2, 1971. Such revenue shall be replaced by imposing statewide taxes, other than ad valorem taxes on real estate, solely on those classes relieved of the burden of paying ad valorem personal property taxes because of the abolition of such taxes subsequent to January 2, 1971. If any taxes imposed for such replacement purposes are taxes on or measured by income, such replacement taxes shall not be considered for purposes of the limitations of one tax and the ratio of 8 to 5 set forth in Section 3(a) of this Article.