There are several Millivilles in Michigan, this particular one is in Lapeer County.
From Michigan Place Names
Lapeer County: in 1837, Horace N. Lathrop, a native of Connecticut, built a sawmill and a grist mill Where the village now stands, and thus gave it its name. He became the supervisor Of Marathon Township in 1839 (the site is now in Oregon Township). Its post office was opened on Jan 17, 1877, with Stephen E. Dickens as its first postmaster [PO Archives]