Monticello, IA has a population of 3,809 and is the 7,669th largest city in the United States. The population density is 603 per sq mi which is 1005% higher than the Iowa average and 566% higher than the national average. The median age in Monticello is 40 which is approximately 6% higher than the Iowa average of 38. In Monticello, 63% of the population over 15 years of age are married, 99% speak English and 1% speak Spanish. 87% of Monticello residents were born in Iowa, 11% were born out of state, 1% were born outside of the United States and 1% were foreign born.