 The county seat was at St. James on Beaver Island.Before the 1836 Treaty of Washington extinguished Native American claim to most of the land in the northwest part of Northern Michigan, the islands were nominally a part of Michilimackinac County (later renamed Mackinac County).In 1840, that portion of Mackinac County lying in the lower peninsula was divided into counties that remained attached for administrative purposes to Mackinac.