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. Sanilac County enjoys seasonal tourism in towns such as Lexington, Port Sanilac, and Carsonville.