Brimfield, IL has a population of 998 and is the 15,179th largest city in the United States. The population density is 1,247 per sq mi which is 461% higher than the Illinois average and 1276% higher than the national average. The median age in Brimfield is 32 which is approximately 14% lower than the Illinois average of 37. In Brimfield, 51% of the population over 15 years of age are married, 99% speak English and 0% speak Spanish. 90% of Brimfield residents were born in Illinois, 10% were born out of state, 0% were born outside of the United States and 0% were foreign born.