625 ILCS 5/3-402.4
The Secretary of State may enter into agreements, compacts, or arrangements with other jurisdictions or agents for such jurisdictions, such as the American Association of Motor Vehicle Administrators, on behalf of this state for allocation or proportional registration of apportionable vehicles in a manner provided in Section 3-402.1 for the purpose of facilitating the administration thereof, and also for the purpose of conforming procedures for proportional registration, pursuant to Sections 3-402.1 and 3-402.2, with those agreed to by two or more additional jurisdictions, including but not limited to, acceptance of base jurisdiction responsibilities for apportional registration and licensing of fleet vehicles in other jurisdiction. In addition, the Secretary of State may adopt and promulgate such rules and regulations as he shall deem necessary to effectuate and administer the provisions of Sections 3-402.1 and 3-402.2. Any reciprocal arrangements or agreements in effect with jurisdictions that cannot grant proportional registration shall remain in force until specifically cancelled by either jurisdiction or until such time that jurisdiction becomes a member of an International Registration Plan (IRP) of which this state is also a member.
625 ILCS 5/3-402.4