Marshfield, WI has a population of 18,410 and is the 2,369th largest city in the United States. The population density is 1,349 per sq mi which is 1444% higher than the Wisconsin average and 1390% higher than the national average. The median age in Marshfield is 41 which is approximately 4% higher than the Wisconsin average of 39. In Marshfield, 58% of the population over 15 years of age are married, 94% speak English and 2% speak Spanish. 76% of Marshfield residents were born in Wisconsin, 19% were born out of state, 1% were born outside of the United States and 4% were foreign born.