Mercer, Wisconsin. Mercer is a town in southern Iron County, Wisconsin, United States. The population was 1,732 at the 2000 census. The census-designated place of Mercer and the unincorporated communities of Carter and Manitowish are located within the town. Mercer identifies itself as the Loon Capital of the World to promote tourism. A wildlife study found Mercer had the highest concentration of common loons in the world. In front of the Mercer Chamber of Commerce's information center, there is a 16-foot, 2,000