50 ILCS 415/2
Whenever it is advantageous and in the public interest to do so, a unit of local government is empowered to effect the net defeasance or the gross defeasance of any outstanding debt lawfully incurred by such unit of local government. When an escrow has been established to effect such net defeasance or gross defeasance of an outstanding debt, the moneys or cash equivalents deposited in such escrow shall be invested and reinvested, pursuant to the direction of the governing authority of such unit of local government, in bonds and other interest bearing obligations of the State of Illinois, or in such accounts, certificates, bills, obligations, shares, pools or other securities as are authorized for the investment of public funds under "An Act relating to certain investments of public funds by public agencies", approved July 23, 1943, as amended; and all interest income or profit derived therefrom in excess of the amounts needed for expenses of administration of the escrow and for payment of all remaining principal and interest until maturity of the debt which is the subject of that escrow shall be transmitted when earned to such unit of local government, pursuant to directions from its governing authority, to be credited to such funds as the governing authority of such unit of local government shall by ordinance or resolution direct.
50 ILCS 415/2