65 ILCS 5/11-148-1

Whenever the territory of any municipality of this state is adjacent to the territory of another state, the municipality may jointly construct a sewage disposal plant, together with all necessary and proper pipes, conduits, and appurtenances within its own corporate limits, and may own, operate, and maintain the plant jointly with any municipality in the adjacent state, for their joint use, on terms and conditions to be agreed upon by the municipalities.