Bay County is located in the U.S. state of Michigan. As of the 2020 Census, the population was 103,856. The county seat is Bay City.

Bay City is a city in and the county seat of Bay County, Michigan, United States. The population was 32,661 at the 2020 census. The city is located just upriver from Saginaw Bay on the Saginaw River. It is the principal city of the Bay City metropolitan area, which is coterminous with Bay County as part of the larger Greater Tri-Cities region of Central Michigan. Several historic bridges cross the Saginaw River in Bay City, including Liberty Bridge, Veterans Memorial Bridge, Independence Bridge, and Lafayette Avenue Bridge.