Gratiot County is a county in the U.S. state of Michigan. As of the 2020 Census, the population was 41,761. The county seat is Ithaca, although its most populous city is Alma. Gratiot County comprises the Alma, MI Micropolitan Statistical Area, which is also part of the Mount Pleasant-Alma, MI Combined Statistical Area. The Gratiot County Courthouse was designed in the classical revival style by Claire Allen, a prominent southern Michigan architect.