Alton, IL has a population of 27,175 and is the 1,592nd largest city in the United States. The population density is 1,757 per sq mi which is 690% higher than the Illinois average and 1839% higher than the national average. The median age in Alton is 38 which is approximately equal to the Illinois average of 37. In Alton, 45% of the population over 15 years of age are married, 98% speak English and 1% speak Spanish. 74% of Alton residents were born in Illinois, 24% were born out of state, 1% were born outside of the United States and 1% were foreign born.