Cairo, IL has a population of 2,559 and is the 9,711th largest city in the United States. The population density is 367 per sq mi which is 65% higher than the Illinois average and 305% higher than the national average. The median age in Cairo is 38 which is approximately 1% higher than the Illinois average of 37. In Cairo, 43% of the population over 15 years of age are married, 98% speak English and 0% speak Spanish. 76% of Cairo residents were born in Illinois, 23% were born out of state, 0% were born outside of the United States and 1% were foreign born.