DeKalb, IL has a population of 43,269 and is the 948th largest city in the United States. The population density is 2,694 per sq mi which is 1112% higher than the Illinois average and 2873% higher than the national average. The median age in DeKalb is 25 which is approximately 34% lower than the Illinois average of 37. In DeKalb, 35% of the population over 15 years of age are married, 84% speak English and 8% speak Spanish. 73% of DeKalb residents were born in Illinois, 17% were born out of state, 0% were born outside of the United States and 9% were foreign born.