Eaton County is a county in the U.S. state of Michigan.As of the 2020 United States Census, the population was 109,175. The county seat is Charlotte. The county was organized in 1837; it was named for John Eaton, who was Secretary of War under US President Andrew Jackson, making it one of Michigan's Cabinet counties.
Sanilac County is a county located in the Thumb region of the U.S. state of Michigan.As of the 2020 Census, the population was 40,611. The county seat is Sandusky. The county was created on September 10, 1822, and was fully organized on December 31, 1849 Sanilac County is considered to be part of the Thumb of Michigan, a subregion of the Flint/Tri-Cities.