Oswego, IL has a population of 33,245 and is the 1,281st largest city in the United States. The population density is 2,232 per sq mi which is 904% higher than the Illinois average and 2363% higher than the national average. The median age in Oswego is 36 which is approximately 3% lower than the Illinois average of 37. In Oswego, 67% of the population over 15 years of age are married, 84% speak English and 10% speak Spanish. 71% of Oswego residents were born in Illinois, 20% were born out of state, 1% were born outside of the United States and 8% were foreign born.