Constitution of the State of Illinois

ARTICLE IX

REVENUE

SECTION 4. REAL PROPERTY TAXATION
 (a) Except as otherwise provided in this Section, taxes
upon real property shall be levied uniformly by valuation
ascertained as the General Assembly shall provide by law.
 (b) Subject to such limitations as the General Assembly
may hereafter prescribe by law, counties with a population of
more than 200,000 may classify or continue to classify real
property for purposes of taxation. Any such classification
shall be reasonable and assessments shall be uniform within
each class. The level of assessment or rate of tax of the
highest class in a county shall not exceed two and one-half
times the level of assessment or rate of tax of the lowest
class in that county. Real property used in farming in a
county shall not be assessed at a higher level of assessment
than single family residential real property in that county.
 (c) Any depreciation in the value of real estate
occasioned by a public easement may be deducted in assessing
such property.
(Source: Illinois Constitution.)