Section 5 ILCS 100/5-10 - Adoption and availability of rules(a) In addition to other rulemaking requirements imposed by law, each agency shall (i) adopt rules of practice setting forth the nature and requirements of all formal hearings and (ii) make available for public inspection all rules adopted by the agency in the discharge of its functions.(b) Each agency shall make available for public inspection all final orders, decisions, and opinions, except those deemed confidential by State or federal statute and any trade secrets.(c) No agency rule is valid or effective against any person or party, nor may it be invoked by the agency for any purpose, until it has been made available for public inspection and filed with the Secretary of State as required by this Act. No agency, however, shall assert the invalidity of a rule that it has adopted under this Act when an opposing party has relied upon the rule.(d) Rulemaking that creates or expands a State mandate on units of local government, school districts, or community college districts is subject to the State Mandates Act. The required Statement of Statewide Policy Objectives shall be published in the Illinois Register at the same time that the first notice under Section 5-40 is published or when the rule is published under Section 5-45 or 5-50.