Monticello, IL has a population of 5,609 and is the 6,003rd largest city in the United States. The population density is 1,470 per sq mi which is 561% higher than the Illinois average and 1522% higher than the national average. The median age in Monticello is 42 which is approximately 11% higher than the Illinois average of 37. In Monticello, 72% of the population over 15 years of age are married, 97% speak English and 1% speak Spanish. 85% of Monticello residents were born in Illinois, 14% were born out of state, 0% were born outside of the United States and 1% were foreign born.