65 ILCS 5/11-111-9
When a specified improvement district has been created by ordinance under Sections 11-111-8 through 11-111-10, the corporate authorities shall have an accurate survey of the work contemplated to be done, made by the city engineer, if there is one, and if not, then by a competent civil engineer. This engineer shall make and file with the municipal clerk, plats, profiles, and estimates of the work to be done. The estimates shall include the cost of all walls or other structures necessary to hold the earth in its proper place and the cost of the fill upon each lot, block, or part thereof, and tract of land within the district, which must be filled under the ordinance. The survey, plat, profile, and estimates shall be used in estimating the benefit to be charged against the lots, blocks, or parts thereof, or tracts of land, within that improvement district by reason of the filing and protection thereof from overflow or unsanitary accumulation of sipe or surface water.
65 ILCS 5/11-111-9