Centralia, IL has a population of 12,696 and is the 3,269th largest city in the United States. The population density is 1,548 per sq mi which is 596% higher than the Illinois average and 1608% higher than the national average. The median age in Centralia is 41 which is approximately 10% higher than the Illinois average of 37. In Centralia, 54% of the population over 15 years of age are married, 96% speak English and 3% speak Spanish. 81% of Centralia residents were born in Illinois, 17% were born out of state, 0% were born outside of the United States and 2% were foreign born.