35 ILCS 200/9-80
The chief county assessment officer in counties with less than 3,000,000 inhabitants shall have the same authority as the township or multi-township assessor to assess and to make changes or alterations in the assessment of property, and shall assess and make such changes or alterations in the assessment of property as though originally made.
Changes by the chief county assessment officer in valuations shall be noted in a column provided, and no change shall be made in the original assessor's figures.
When the chief county assessment officer or his or her deputy views property for the purposes of assessing the property or determining whether a change or alteration in the assessment of the property is required, he or she shall give notice to the township assessor by U.S. Mail at least 5 days but not more than 30 days prior to the viewing, so that the assessor may arrange to be present at the viewing , except if the township or multi-township assessor fails to timely return the assessment books or workbooks as required by Section 9-230 . He or she shall also give notice to owners of the properties by means of notices in a paper of general circulation in the township. The notices shall state the chief county assessment officer's intention to view the property but need not specify the date and time of the viewing. When the chief county assessment officer or his or her deputy is present at the property to be viewed, immediately prior to the viewing, he or she shall make a reasonable effort to ascertain if the owner or his or her representative, or the assessor, are on the premises and to inform them of his or her intention to view the property. Failure to provide notice to the township assessor and owner shall not of and by itself invalidate any change in an assessment. A viewing under this Section and Section 9-155 means actual viewing of the visible property in its entirety from, on or at the site of the property.
All changes and alterations in the assessment of property shall be subject to revision by the board of review in the same manner that original assessments are reviewed.
35 ILCS 200/9-80