Marshfield is in Wood and Marathon counties in the 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 18,929 at the 2020 census. Of this, 18,119 were in Wood County, and 810 were in Marathon County. The city is part of the United States Census Bureau's Marshfield-Wisconsin Rapids Micropolitan Statistical Area, which includes all of Wood County.