Flossmoor, IL has a population of 9,215 and is the 4,190th largest city in the United States. The population density is 2,517 per sq mi which is 1032% higher than the Illinois average and 2678% higher than the national average. The median age in Flossmoor is 48 which is approximately 29% higher than the Illinois average of 37. In Flossmoor, 63% of the population over 15 years of age are married, 83% speak English and 2% speak Spanish. 66% of Flossmoor residents were born in Illinois, 24% were born out of state, 2% were born outside of the United States and 8% were foreign born.