Wausau is a city in and the county seat of Marathon County, Wisconsin, United States, along the Wisconsin River. As of the 2020 census, it had a population of 39,994. It is the core city of the Wausau metropolitan area, which includes all of Marathon County and had a population of 138,013 in 2020. The city's suburbs include Schofield, Weston, Mosinee, Maine, Rib Mountain, Kronenwetter, and Rothschild.