Birch is a town in Lincoln County, Wisconsin, United States. As of the 2010 census, the town had a population of 594, down from 801 at the 200…Birch is a town in Lincoln County, Wisconsin, United States. As of the 2010 census, the town had a population of 594, down from 801 at the 2000 census. The unincorporated community of Irma is located in the town.