Montmorency County is a county located in the U.S. state of Michigan. As of the 2020 census, the population was 9,153, making it the second-least populous county in Michigan's Lower Peninsula, behind its southern neighbor, Oscoda County. The county seat is Atlanta. Montmorency County is part of Northern Michigan, and is part of the Lake Huron watershed. The Thunder Bay River, which drains much of the county, flows to Lake Huron's Thunder Bay at Alpena.