Affton, MO has a population of 22,060 and is the 1,971st largest city in the United States. The population density is 4,620 per sq mi which is 5248% higher than the Missouri average and 4999% higher than the national average. The median age in Affton is 41 which is approximately 6% higher than the Missouri average of 38. In Affton, 55% of the population over 15 years of age are married, 87% speak English and 1% speak Spanish. 72% of Affton residents were born in Missouri, 17% were born out of state, 0% were born outside of the United States and 11% were foreign born.