Marshfield is a city in Wood County and extending into Marathon County in the U.S. state of Wisconsin. It is located at the intersection of U.S. Highway 10, Highway 13 and Highway 97. The largest city in Wood County, its population was 19,118 at the 2010 census. Of this, 18,218 were in Wood County, and 900 were in Marathon County. The city forms one of the core areas of the United States Census Bureau's Marshfield-Wisconsin Rapids Micropolitan Statistical Area, which includes all of Wood County (2010 population: 74,749).