Frontenac, MO has a population of 3,527 and is the 8,013th largest city in the United States. The population density is 1,228 per sq mi which is 1321% higher than the Missouri average and 1255% higher than the national average. The median age in Frontenac is 47 which is approximately 24% higher than the Missouri average of 38. In Frontenac, 74% of the population over 15 years of age are married, 93% speak English and 1% speak Spanish. 54% of Frontenac residents were born in Missouri, 37% were born out of state, 3% were born outside of the United States and 6% were foreign born.