75 ILCS 5/2-4
In the event a village not under a commission form of government converts to a commission form of government or becomes a city, or a village or city under a commission form of government changes to a village or city not under a commission form of government, the incumbent board of library trustees of the village or the city board of library trustees of the city, as the case may be, shall thereupon become the library trustees of the village or city, whichever is the form of the new municipal governmental organization, and shall serve as such until the term of office for which each had been elected or appointed expires, and until his successor has been elected or appointed according to law and has qualified for such office. Thereafter, new or additional library trustees shall be elected or appointed, or the number of trustees reduced, so that the number of trustees holding office at any one time shall conform as nearly as is practicable to the number of library trustees required by law for the particular city or village as it is organized after changing its form or classification of municipal government.
The ceiling upon the annual public library tax existing prior to the conversion or change in form of municipal government and any special tax previously authorized by the electors shall be applicable after the conversion or change.
Any existing bond issue and the special tax therefor shall not be affected by such conversion or change and shall continue in full force and effect under the law governing such bond issue and special tax.
75 ILCS 5/2-4