Eldorado, IL has a population of 4,134 and is the 7,299th largest city in the United States. The population density is 1,651 per sq mi which is 643% higher than the Illinois average and 1722% higher than the national average. The median age in Eldorado is 35 which is approximately 5% lower than the Illinois average of 37. In Eldorado, 54% of the population over 15 years of age are married, 99% speak English and 0% speak Spanish. 74% of Eldorado residents were born in Illinois, 25% were born out of state, 0% were born outside of the United States and 0% were foreign born.