Fairbury, IL has a population of 3,610 and is the 7,904th largest city in the United States. The population density is 1,970 per sq mi which is 786% higher than the Illinois average and 2074% higher than the national average. The median age in Fairbury is 40 which is approximately 8% higher than the Illinois average of 37. In Fairbury, 56% of the population over 15 years of age are married, 93% speak English and 5% speak Spanish. 79% of Fairbury residents were born in Illinois, 18% were born out of state, 0% were born outside of the United States and 2% were foreign born.