Mich. Comp. Laws § 123.739

Sec. 9. No county shall have the power to furnish water service, sewage disposal service or refuse service to the individual users within any municipality without its consent. The foregoing shall not prevent the county from extending any sewage disposal system or refuse system into any municipality where in the opinion of a majority of the members elect of the board of supervisors the same is necessary to protect health or property in any adjacent municipality and from furnishing sewage disposal or refuse services to individual users therein. Any such extensions may be constructed along with the construction of the original system or thereafter.