Michigan Compiled Laws, Chapter 51. Sheriffs § 51.71

Sec. 71.  The sheriff of each county shall, as soon as may be after entering upon the execution of his office, appoint some proper person under sheriff of the same county, who shall also be a general deputy, to hold during the pleasure of such sheriff;  and as often as a vacancy shall occur in the office of such under sheriff, or he become incapable of executing the same, another shall in like manner be appointed in his place.