Mich. Comp. Laws § 129.144: Authorization by resolution.

Sec. 4.

A county treasurer shall not enter into a contract with a local unit for deposit of money in an investment pool until authorized to establish an investment pool by a resolution of the county board of commissioners of that participating county.

The treasurer or other chief fiscal officer of a local unit shall not enter into a contract for deposit of money in an investment pool until authorized by a resolution of the governing body of that local unit.