Marseilles, IL has a population of 4,892 and is the 6,572nd largest city in the United States. The population density is 540 per sq mi which is 143% higher than the Illinois average and 496% higher than the national average. The median age in Marseilles is 35 which is approximately 7% lower than the Illinois average of 37. In Marseilles, 58% of the population over 15 years of age are married, 99% speak English and 1% speak Spanish. 80% of Marseilles residents were born in Illinois, 20% were born out of state, 0% were born outside of the United States and 0% were foreign born.