The system serves over 44,000 people through 4,700 water meters and almost 2,500 wastewater connections.
Under the agreement, Aqua Illinois will purchase the system for up to $22m pending an evaluation of assets.
Subject to Illinois Commerce Commission approval, the transaction includes a process by which three appraisers will be hired to set the final value of the system.
With the transaction, which was expected to close in the summer of 2015, the company will complete 25 municipal acquisitions since 1992.
The company has also agreed for $10m in capital investments to the system to construct an interconnection with Glenview to purchase Lake Michigan water from Glenview/Wilmette by 2020.
Aqua Illinois operations vice president Craig Blanchette said, "Aqua Illinois is glad to be able to provide the residents and businesses of North Maine with quality water and wastewater services, reasonable rates and excellent customer service."
"With more than 125 years of experience in the water industry, we have the operational capacity, technical expertise and resources needed to meet the needs of NMU customers," Blanchette added.
