Michigan Compiled Laws, Chapter 600. Revised Judicature Act of 1961 § 600.1641

Sec. 1641. (1) Except as provided in subsection (2), if causes of action are joined, whether properly or not, venue is proper in any county in which either cause of action, if sued upon separately, could have been commenced and tried, subject to separation and change as provided by court rule.

(2) If more than 1 cause of action is pleaded in the complaint or added by amendment at any time during the action and 1 of the causes of action is based on tort or another legal theory seeking damages for personal injury, property damage, or wrongful death, venue shall be determined under the rules applicable to actions in tort as provided in section 1629.  1