Sanilac County is a county located in the U.S. state of Michigan. As of the 2010 census, the population was 43,114. The county seat is Sandusky. The county, which is part of the Thumb region, was created on September 10, 1822, and was fully organized in 1848.Sanilac County is considered to be part of the Thumb of Michigan, which in turn is a subregion of the Flint/Tri-Cities. Sanilac County enjoys seasonable tourism in towns such as Lexington, Port Sanilac, and Carsonville.