Emmet County was formed April 1, 1840, from Mackinac County. It was first named Tonedagana County and renamed Emmet County on March 8, 1843. Emmet County remained attached to Mackinac County for administrative purposes until county government was organized in 1853. The county was named for the Irish patriot Robert Emmet, who was hanged as a traitor to the British government at the age of 23.
Source : Emmet County Wikipedia entry.