30 ILCS 767/15-5
As used in this Act:
"Grant index" means a figure for each public library equal to one minus the ratio of the public library's equalized assessed valuation per capita to the equalized assessed valuation per capita of the public library located at the 90th percentile for all public libraries in the State. The grant index shall be no less than 0.35 and no greater than 0.75 for each public library; provided that the grant index for public libraries whose equalized assessed valuation per capita is at the 99th percentile and above for all public libraries in the State shall be 0.00.
"Public library" means the governmental unit of any free and public library (i) established under the Illinois Local Library Act, the Public Library District Act of 1991, the Illinois Library System Act, or the Village Library Act or (ii) maintained and operated by a unit of local government. "Public library" does not include any private library.
"Public library construction project" means the acquisition, development, construction, reconstruction, rehabilitation, improvement, architectural planning, installation, maintenance, and upkeep of capital facilities consisting of buildings, structures, durable equipment, and land for public library purposes.
30 ILCS 767/15-5