Mich. Comp. Laws § 600.8119

Sec. 8119. (1) The twelfth district consists of the county of Jackson except the city of Jackson, is a district of the second class and has 2 judges. However, due to section 8180, effective January 1, 1986, the twelfth district consists of the county of Jackson, is a district of the first class, and has 4 judges. (2) The thirteenth district consists of the city of Jackson, is a district of the third class, and has 2 judges. However, due to section 8180, effective January 1, 1986, the thirteenth district will no longer exist.