55 ILCS 5/5-30018
A certificate of appropriateness from a preservation commission established pursuant to this Division shall be required before any significant alteration, construction, demolition or removal that affects pending or designated landmarks and preservation districts is undertaken. Such a certificate is required for all such actions from the date a nomination in proper form for designation is submitted to the preservation commission. The preservation ordinance enacted by the county board shall give the preservation commission one or the other of the following powers: (1) final authority to deny a certificate of appropriateness upon a finding that the proposed action will adversely affect the historic, archaeological, architectural, or scenic significance of a landmark or preservation district; or (2) authority to delay the issuance of a certificate of appropriateness for a reasonable period of time while negotiations between the property owner and the preservation commission are undertaken to lessen the effect of the proposed action on the historic, archaeological, architectural, or scenic significance of the landmark or preservation district. The preservation commission may hold a public hearing on an application for a certificate of appropriateness in the same manner as provided in Section 5-30014, and conduct the hearing on appropriateness in the same manner as provided in Section 5-30015.
55 ILCS 5/5-30018