Gillespie, IL has a population of 3,323 and is the 8,302nd largest city in the United States. The population density is 2,238 per sq mi which is 907% higher than the Illinois average and 2371% higher than the national average. The median age in Gillespie is 43 which is approximately 14% higher than the Illinois average of 37. In Gillespie, 58% of the population over 15 years of age are married, 98% speak English and 0% speak Spanish. 82% of Gillespie residents were born in Illinois, 17% were born out of state, 0% were born outside of the United States and 1% were foreign born.