Amends the Illinois Insurance Code. Establishes reimbursement rates for mental health and substance use disorder treatment services for all group or individual policies of accident and health insurance or managed care plans that are amended, delivered, issued, or renewed on or after January 1, 2027 or for any contracted third party administering the behavioral health benefits for the insurer. Requires a group or individual policy of accident and health insurance or managed care plan that is amended, delivered, issued, or renewed on or after January 1, 2026 or any contracted third party administering the behavioral health benefits for the insurer to cover certain medically necessary mental health and substance use disorder treatment services. Provides that, if the Department of Insurance determines that an insurer or a contracted third party administering the behavioral health benefits for the insurer has violated a provision concerning mental health and substance use parity, the Department shall by order assess a civil penalty of $1,000 for each violation. Excludes certain health care plans serving Medicaid populations who are enrolled under the Illinois Public Aid Code or under the Children's Health Insurance Program Act from provisions concerning mental health and substance use parity. Requires the Department to review the impact of the proposed mental health and substance abuse mandate on network adequacy for mental health and substance use disorder treatment and access to affordable mental health and substance use care. Permits the Department to examine out-of-network utilization and out-of-pocket costs for insureds for mental health and substance use treatment and services for all plans to compare with in-network utilization. Amends the State Employees Group Insurance Act of 1971, the Counties Code, the Illinois Municipal Code, and the School Code to require coverage under those provisions. Effective immediately.