Northfield, IL has a population of 5,374 and is the 6,157th largest city in the United States. The population density is 1,664 per sq mi which is 649% higher than the Illinois average and 1737% higher than the national average. The median age in Northfield is 49 which is approximately 30% higher than the Illinois average of 37. In Northfield, 63% of the population over 15 years of age are married, 79% speak English and 4% speak Spanish. 65% of Northfield residents were born in Illinois, 19% were born out of state, 1% were born outside of the United States and 16% were foreign born.