Creates the Mental Health and Substance Use Disorder Rate Equity Act. Provides that, beginning in 2023, and every State fiscal year thereafter, the General Assembly shall appropriate sufficient funds to the Department of Human Services to ensure grants to community-based prevention organizations and providers of mental health and substance use disorder treatment under community service grant programs will be adjusted upward by an amount equal to the Consumer Price Index-U from the previous year, not to exceed 2% in any State fiscal year. Requires similar appropriations to be made, beginning in 2024, to increase the reimbursement rates for certified community mental health centers and behavioral health clinics and licensed or certified community-based substance use disorder treatment providers. Amends the Substance Use Disorder Act. Requires the Department of Human Services to implement incremental rate increases for all community-based substance use disorder treatment and intervention services beginning July 1, 2021 and every State fiscal year thereafter. Amends the Mental Health and Developmental Disabilities Administrative Act. Requires the Department to implement incremental rate increases for all community-based mental health treatment services beginning July 1, 2021 and every State fiscal year thereafter. Amends the Illinois Public Aid Code. Provides that, beginning on July 1, 2021, reimbursement rates for psychiatric and behavioral health services provided by community mental health centers or behavioral health clinics shall be increased by 9%. Requires incremental rate increases beginning July 1, 2022 and every State fiscal year thereafter. Amends the Illinois Administrative Procedure Act. Permits the Departments of Human Services and Healthcare and Family Services to adopt emergency rules. Effective immediately.