Oglesby, IL has a population of 3,834 and is the 7,634th largest city in the United States. The population density is 945 per sq mi which is 325% higher than the Illinois average and 943% higher than the national average. The median age in Oglesby is 39 which is approximately 5% higher than the Illinois average of 37. In Oglesby, 63% of the population over 15 years of age are married, 96% speak English and 1% speak Spanish. 92% of Oglesby residents were born in Illinois, 6% were born out of state, 0% were born outside of the United States and 2% were foreign born.