Mich. Comp. Laws § 259.811
The board shall certify to each participating county the amount to be raised by them, and the counties comprising the authority shall include the certified amount to be raised in their next ensuing budget and shall pay the amounts so certified from any funds they have available including the proceeds of a tax the county is authorized to levy on the taxable property within their respective jurisdiction. The tax shall not exceed 3/4 mill on each dollar of assessed valuation as last equalized by the state. In computing the total tax to be levied, the assessed valuation of any unit of government within the county shall not be used more than once. The limitation of section 6 of article 9 of the state constitution shall not apply to taxes imposed by the board and levied by the counties comprising the authority.
MCL 259.811