Amends the General Provisions Article of the Illinois Pension Code. Provides that the amendatory Act may be referred to as the Fossil Fuel Divestment Act. With regard to the pension funds and retirement systems established under the General Assembly, Chicago Police, Chicago Firefighter, Illinois Municipal Retirement Fund (IMRF), Chicago Municipal, Chicago Laborers', State Employees, State Universities, Downstate Teachers, or Judges Article of the Code, prohibits investment of pension system assets in fossil fuel companies. Requires pension systems to adopt an update to its written investment policies if necessary. Requires pension systems to divest any holdings of stocks, securities, or other obligations of a fossil fuel company. Provides that, beginning one year after the effective date of the amendatory Act, the board of trustees of a pension system shall ensure that the pension system does not invest in any indirect investment vehicle unless the board of trustees is satisfied that the investment vehicle is unlikely to have more than 2% of its assets invested in coal, oil, or gas producers. Requires pension systems to post on its publicly accessible website information detailing all its holdings in the public market and private equity investments. Requires pension systems to annually issue a report reviewing its environmental, social, and governance investment policy. Sets forth definitions and other provisions. Amends the State Mandates Act to require implementation without reimbursement. Effective immediately.