Mich. Comp. Laws § 45.20: Division or alteration of county; lands within county limits.

Sec. 20.

When a county seized of lands shall be divided into 2 or more counties, or shall be altered in its limits, by annexing a part of its territory to any other county or counties, each county shall become seized to its own use, of such part of said lands as shall be included within its limits, as settled by such division or alteration.