Swansea, IL has a population of 13,722 and is the 3,044th largest city in the United States. The population density is 2,129 per sq mi which is 858% higher than the Illinois average and 2250% higher than the national average. The median age in Swansea is 42 which is approximately 11% higher than the Illinois average of 37. In Swansea, 63% of the population over 15 years of age are married, 98% speak English and 1% speak Spanish. 61% of Swansea residents were born in Illinois, 35% were born out of state, 3% were born outside of the United States and 2% were foreign born.