65 ILCS 5/11-140-1
In every municipality with a population of 100,000 or less which has a sewage system but has no adequate outlet therefor, or any proper disposition of the sewage thereof, without constructing an outlet sewer the terminus of which will be outside the corporate limits of the municipality, the corporate authorities thereof may (1) construct an outlet sewer, wholly without, or partially within and partially without the corporate limits of the municipality into which the sewers throughout the municipality are to empty, and through which the sewers are to discharge their sewage for proper disposition and sanitary benefits, (2) construct reservoirs, erect pumping works, machinery, and plants for the treatment of the sewage within or without the corporate limits of the municipality, (3) acquire the necessary land and machinery for these purposes, and (4) otherwise provide for discharge of the municipality's sewage into channels that will promote the health and improve the sanitary condition of and accomplish the purpose of an outlet sewer for the municipality. The cost of exercising the powers conferred by this section shall be borne by special assessment or by special taxation upon the property in those portions of the municipality the sewers in which are ultimately to find their outlet through the outlet sewer so constructed.
65 ILCS 5/11-140-1