The county was set off in 1843, and organized in 1848. It had been part of Chippewa and Mackinac counties; and it was thereafter split to create Gogebic County. See List of Michigan counties. The name is said to be derived from a Native American word "Nondon-organ" meaning "hunting river and which appeared as named for a river called "Nantounagon" on a 1670 French map. Alternatively, it is said to be derived from the Ojibwa "onagon" which means "dish" or "bowl. See List of Michigan county name etymologies.
Perhaps, the name Ontonagon means both hunting and bowl. There is a local story that says a young maiden put a dish or bowl into the Ontonagan River to clean it. It escaped her and drifted down the river. She cried "My bowl! My bowl! Please hunt [search] for my bowl!". So, the river was called Ontonagon. The Ontonagan River Valley is, also, shaped like a basin or bowl.
There were 3,456 households out of which 23.60% had children under the age of 18 living with them, 53.60% were married couples living together, 6.30% had a female householder with no husband present, and 35.60% were non-families. 31.50% of all households were made up of individuals and 16.00% had someone living alone who was 65 years of age or older. The average household size was 2.21 and the average family size was 2.75.
In the county the population was spread out with 20.20% under the age of 18, 4.70% from 18 to 24, 23.30% from 25 to 44, 30.20% from 45 to 64, and 21.60% who were 65 years of age or older. The median age was 46 years. For every 100 females there were 102.70 males. For every 100 females age 18 and over, there were 101.50 males.
The median income for a household in the county was $29,552, and the median income for a family was $36,690. Males had a median income of $31,884 versus $21,121 for females. The per capita income for the county was $16,695. About 5.80% of families and 10.40% of the population were below the poverty line, including 12.90% of those under age 18 and 10.10% of those age 65 or over.
(information as of September 2005)