75 ILCS 5/5-6
If the trustees deem it best, in order to provide and secure the necessary money to do any or all of the things they are authorized to do in and by this Article, they may with the approval of the corporate authorities at any time borrow money and execute a mortgage on an existing library building or site owned or being purchased, or on a library building being constructed, for an amount not exceeding 75% of the value thereof as improved, and the money so obtained shall be used exclusively for the purchase of a site or a building or for the construction of a building for library purposes or for the remodeling, repairing or improving of such existing library building or building of an addition thereto or for the erection of a new library building or for purchase and improvement of a site or building adjoining or adjacent to the existing site and building or the purchase of necessary equipment for such library, as provided in the plan. The proceeds of any special tax levied under Section 5-3 may be applied in whole or in part in payment of any mortgage indebtedness so incurred. The levy of a tax hereunder for the purpose of meeting such mortgage and interest, or the principal and interest on bonds issued hereunder, or for the accumulation of a fund as hereinabove provided, shall not be included in the aggregate amount of taxes as limited by Division 3 of Article 8 of the Illinois Municipal Code nor shall it affect any appropriation made, or to be made, for the support of the library. This Section shall not apply to any city having over 500,000 inhabitants.
75 ILCS 5/5-6