The Oil and Gas Division of the Department of Natural Resources, Office of Mines and Minerals is the regulatory entity in Illinois.
They are responsible for the permitting, drilling, operating, and plugging of oil and gas wells in the state. Additionally, they regulate the injection of fluids into underground injection wells, and are charged with cleaning up abandoned wells in the state.
Another good resource is the Illinois Oil and Gas Association website.
Illinois Oil & Gas Association
IOGA was founded in 1944 to provide an agency through which oil and gas producers, land owners, royalty owners, and others who may be directly or indirectly affected by or interested in oil and gas development and productionin Illinois may protect, preserve and advance their common interests.