620 ILCS 45/1
The county board of each county having a population of less than 1,000,000 may in the manner hereinafter provided, establish and maintain airports and landing fields and other auxiliary institutions connected with the same within the limits of such county for the use and benefit of the inhabitants thereof and may levy a tax subject to such further limitation as may be occasioned by the issue of bonds as hereinafter provided, not to exceed .25 per cent of the value, as equalized or assessed by the Department of Revenue, annually on all taxable property of such county, such tax to be levied and collected in like manner with the general taxes of such county, and to form, when collected, a fund to be known as the "County Airport Fund". Such tax shall be in addition to all other taxes which such county is now or hereafter may be authorized to levy on the aggregate valuation of all property within such county and shall not be included within the rate for general county purposes, but shall be in addition thereto and exclusive thereof. The foregoing limitations upon tax rates may be increased or decreased under the referendum provisions of the General Revenue Law of Illinois.
620 ILCS 45/1