Cortland, IL has a population of 4,135 and is the 7,296th largest city in the United States. The population density is 1,133 per sq mi which is 397% higher than the Illinois average and 1151% higher than the national average. The median age in Cortland is 30 which is approximately 19% lower than the Illinois average of 37. In Cortland, 58% of the population over 15 years of age are married, 83% speak English and 14% speak Spanish. 76% of Cortland residents were born in Illinois, 12% were born out of state, 0% were born outside of the United States and 11% were foreign born.