65 ILCS 5/11-118-3
Whenever revenue bonds have been issued under this Division 118, the entire revenue received thereafter from the operation of the heating plant and system shall be deposited in a separate fund, designated the heating fund of the municipality of ..... This revenue shall be used only in paying the cost of maintenance and operation of the heating plant and system and the principal of interest upon the bonds issued under this Division 118.
Rates charged for heating shall be sufficient to pay the cost of maintenance and operation and to pay the principal of and interest upon all bonds issued under this Division 118, for the construction of the heating plant and system. These rates shall not be reduced while any of these bonds are unpaid.
Revenue bonds issued under this Division 118 may be redeemed at any interest-paying date, by proceeding as follows: (1) a written notice shall be mailed to the holder of such a bond 30 days prior to an interest-paying date, notifying the holder that the bond will be redeemed on the next interest-paying date; or (2) if the holder of such a bond is unknown, then a notice describing the bond to be redeemed and the date of its redemption shall be published 30 days prior to an interest-paying date in one or more newspapers published in the municipality, or, if no newspaper is published therein, then in one or more newspapers with a general circulation within the municipality. In municipalities with less than 500 population in which no newspaper is published, publication may instead be made by posting a notice in 3 prominent places within the municipality. When notice has been mailed to the holder of such a bond, or when notice has been published in a newspaper, in case the holder of the bond is unknown, the bond shall cease bearing interest from and after the next interest-paying date.
65 ILCS 5/11-118-3