Troy, IL has a population of 10,041 and is the 3,933rd largest city in the United States. The population density is 1,898 per sq mi which is 754% higher than the Illinois average and 1995% higher than the national average. The median age in Troy is 33 which is approximately 11% lower than the Illinois average of 37. In Troy, 64% of the population over 15 years of age are married, 97% speak English and 2% speak Spanish. 56% of Troy residents were born in Illinois, 40% were born out of state, 1% were born outside of the United States and 3% were foreign born.