Green Bay is a city in Brown County, Wisconsin, United States, and its county seat. It is located at the head of Green Bay (known locally as "the bay of Green Bay"), a sub-basin of Lake Michigan at the mouth of the Fox River. As of the 2020 census, the city had a population of 107,395, making it the third-most populous city in Wisconsin, after Milwaukee and Madison, and the third-most populous city on Lake Michigan, after Chicago and Milwaukee. Green Bay is the principal city of the Green Bay metropolitan area, which covers Brown, Kewaunee, and Oconto counties and had a population of 320,050 in 2020.