525 ILCS 30/17
All public agencies shall recognize that the protection of nature preserves, buffer areas and registered areas is the public policy of the State and shall avoid the planning of any action that would adversely affect them.
It shall be the public policy of each agency of State or local government to utilize its authority in furtherance of the purposes of this Act, and to evaluate, through a process of consultation with the Department, whether the actions, including capital projects, that are authorized, funded, or carried out by the agency of State or local government are likely to result in the destruction or adverse modification of any natural area that is registered under this Act or identified in the Illinois Natural Areas Inventory.
The evaluation shall be conducted early in the planning of a proposed action. If the proposed action is found likely to have an adverse impact on a natural area, the agency shall study the proposed action to determine possible methods of eliminating or mitigating the adverse impact. Before implementing any action, the agency shall attempt to mitigate or eliminate any adverse impacts in a manner consistent with the planned action. The Department, Commission, or any affected person may seek a writ of mandamus to compel an agency of State or local government to engage in the evaluation and study required by this Section.
525 ILCS 30/17