65 ILCS 5/9-2-45
The officer specified in Section 9-2-44 shall estimate what proportion of the total cost of such improvement will be of benefit to the public, and what proportion thereof will be of benefit to the property to be benefited, and to apportion the total cost between the municipality and that property, so that each will bear its relative equitable proportion. Having found these amounts, such officer shall apportion and assess the amount so found to be of benefit to the property, upon the several lots, blocks, tracts, and parcels of land, in the proportion in which they will be severally benefited by the improvement. No lot, block, tract, or parcel of land shall be assessed a greater amount than it will be actually benefited, except that the apportionment and assessment shall include the anticipated fees for the recording of documents as provided in this Article. When the proposed improvement is for the construction of a sewer, it is the duty of such officer to investigate and report the district which will be benefited by the proposed sewer, describing the district by boundaries.
Where the improvement is to be constructed with aid from any agency of the Federal Government, or other governmental agency, the proportion of the total cost of the improvement to be raised by the municipality in addition to such aid shall be the amount allocated between public benefits and benefits of the property affected as above provided.
65 ILCS 5/9-2-45