Mosinee is a city in Marathon County, Wisconsin. It is part of the Wausau, Wisconsin Metropolitan Statistical Area. The population was 4,452 at the time of the 2020 census.

Marathon County is a county located in the U.S. state of Wisconsin. As of the 2020 census, the population was 138,013. Its county seat is Wausau. It was founded in 1850, created from a portion of Portage County. At that time the county stretched to the northern border with the upper Michigan peninsula. It is named after the battlefield at Marathon, Greece.