St. Johns, AZ has a population of 3,542 and is the 7,989th largest city in the United States. The population density is 137 per sq mi which is 138% higher than the Arizona average and 51% higher than the national average. The median age in St. Johns is 36 which is approximately 4% lower than the Arizona average of 37. In St. Johns, 55% of the population over 15 years of age are married, 88% speak English and 9% speak Spanish. 65% of St. Johns residents were born in Arizona, 32% were born out of state, 0% were born outside of the United States and 3% were foreign born.