[1][5] It is also the westernmost county in United States that lies within the Eastern Time Zone.

In 1843, Michigan's Upper Peninsula was divided into Mackinac, Chippewa, Marquette, Schoolcraft, Delta, and Ontonagon Counties.

[8] The Ontonagan Copper Boulder was removed from the west branch of the Ontonagon River and transported in 1842 to Detroit where it was weighed at 3708 pounds, thence to the Smithsonian Institution.

The name is said to be loosely derived from an Ojibwe language word noojitoon ziibi, meaning "hunting river.

Ontonagon County is located in the western Upper Peninsula, along the shore of Lake Superior.

At a longitude of 89.5°W, it is the westernmost county in the United States contained entirely within the Eastern Time Zone.

Ontonagon County operates the County jail, maintains rural roads, operates the major local courts, records deeds, mortgages, and vital records, administers public health regulations, and participates with the state in the provision of social services.

The county board of commissioners controls the budget and has limited authority to make laws or ordinances.

In Michigan, most local government functions – police and fire, building and zoning, tax assessment, street maintenance etc.