Northfield, MN has a population of 20,405 and is the 2,125th largest city in the United States. The population density is 2,401 per sq mi which is 3781% higher than the Minnesota average and 2550% higher than the national average. The median age in Northfield is 27 which is approximately 28% lower than the Minnesota average of 38. In Northfield, 44% of the population over 15 years of age are married, 88% speak English and 6% speak Spanish. 54% of Northfield residents were born in Minnesota, 37% were born out of state, 1% were born outside of the United States and 8% were foreign born.