Birnamwood is a village in Marathon and Shawano counties in the U.S. state of Wisconsin. It is part of the Wausau, Wisconsin Metropolitan Statistical Area. The population was 818 at the 2010 census. Of this, 802 were in Shawano County, and 16 were in Marathon County. The village is located mostly within the town of Birnamwood in Shawano County; only a small portion extends into the town of Norrie in adjacent Marathon County.