St. Peters, MO has a population of 55,820 and is the 716th largest city in the United States. The population density is 2,486 per sq mi which is 2778% higher than the Missouri average and 2644% higher than the national average. The median age in St. Peters is 39 which is approximately 1% higher than the Missouri average of 38. In St. Peters, 63% of the population over 15 years of age are married, 94% speak English and 2% speak Spanish. 69% of St. Peters residents were born in Missouri, 26% were born out of state, 1% were born outside of the United States and 3% were foreign born.